ES2992660T3 - Method and apparatus for chroma intra prediction in video coding - Google Patents

Abstract

Devices and methods for intra-directional prediction for the chromatic component of an image are provided. The method includes obtaining an initial intra prediction mode of the chromatic component and deriving an intra chromatic prediction mode (intraPredModeC) from a look-up table (LUT) using the initial intra prediction mode of the chromatic component. The chromatic component has different subsampling ratios in horizontal and vertical directions. The method further includes performing wide-angle mapping in the intra chromatic prediction mode (intraPredModeC) to obtain a modified intraPredModeC; obtaining an intraPredAngle parameter for the chromatic component based on the modified intraPredModeC; and obtaining predicted samples of the chromatic component based on the intraPredAngle parameter. The method provides the minimum number of entries in the LUT that is used to determine the intra chromatic prediction mode from the initial intra chromatic prediction mode. (Automatic translation with Google Translate, no legal value)

Description

DESCRIPTION

Method and apparatus for chroma intraprediction in video coding

Technical field

Embodiments of the present application (description) relate generally to the field of image processing and more particularly to chroma intra prediction methods in video coding.

Background

Video coding (video encoding and decoding) is used in a wide range of digital video applications, for example, digital TV broadcasting, video streaming over the Internet and mobile networks, real-time conversation applications such as video chat, video conferencing, DVD and Blu-ray discs, video content acquisition and editing systems, and video cameras for security applications.

The amount of video data required to represent even a relatively short video can be substantial, which can result in difficulties when the data has to be transmitted or communicated over a communications network with limited bandwidth capacity. Therefore, video data is usually compressed before being communicated over today's telecommunications networks. The size of a video could also be an issue when the video is stored on a storage device because memory resources may be limited. Video compression devices often use software and/or hardware at the source to encode the video data before transmission or storage, thereby decreasing the amount of data required to represent digital video images. The compressed data is then received at the destination by a video decompression device that decodes the video data. With limited network resources and ever-increasing demands for higher video quality, improved compression and decompression techniques that improve the compression ratio with little or no sacrifice in image quality are desirable.

BRO SS B Y CO L.:”Versatile Video Coding (Draft 4)”, 13th JV E T Meeting: 20190109 - 20190118; MARRAKECH; (THE JOINT VIDEO SCANNING TEAM OF ISO/IEC JTC1/SC29/WG11 AND ITU-T SG.16), n° JVET-M1001 17 March 2019 (2019-03-17), XP030255166, releases the draft text of the video coding specification.

Compendium

Embodiments of the present application provide apparatus and methods for encoding and decoding according to the independent claims.

The above and other objects are achieved by the subject matter of the independent claims. Other embodiments are apparent from the dependent claims, the description and the figures. The invention is set forth in the appended claims.

Embodiments of the present invention provide the minimum number of entries in the LUT that is used to determine the chroma intra prediction mode from the initial chroma intra prediction mode. The initial chroma intra prediction mode may be equal to the initial luma intra prediction mode. This is achieved by the order of the steps performed, i.e. by the assignment of the chrominance intra prediction mode to the luma mode which is performed before the wide angle assignment.

Details of one or more embodiments are set forth in the accompanying drawings and description below. Other features, objects and advantages will become apparent from the description, drawings and claims.

Brief description of the drawings

In the following embodiments of the invention they are described in more detail with reference to the accompanying figures and drawings, in which:

Fig. 1A is a block diagram showing an example of a video coding system configured to implement embodiments of the invention;

Fig. 1B is a block diagram showing another example of a video coding system configured to implement embodiments of the invention;

Fig. 2 is a block diagram showing an example of a video encoder configured to implement embodiments of the invention;

Fig. 3 is a block diagram showing an exemplary structure of a video decoder configured to implement embodiments of the invention;

Fig. 4 is a block diagram illustrating an example of an encoding apparatus or a decoding apparatus;

Fig. 5 is a block diagram illustrating another example of an encoding apparatus or a decoding apparatus;

Fig. 6 is a drawing showing intraprediction angular directions and associated intraprediction modes in the VTM-4 and VVC draft specification v.4;

Fig. 7 is a drawing showing luma and chroma color planes for YUV 4:2:0 and YUV 4:2:2 chroma formats;

Fig. 8 shows an example of the case where IntraPredModeC is derived from IntraPredModeY where IntraPredModeY is a wide-angle intraprediction mode and IntraPredModeC is a non-wide-angle intraprediction mode;

Fig. 9 shows an example of the case where IntraPredModeC is derived from IntraPredModeY where IntraPredModeY is a non-wide-angle intraprediction mode and IntraPredModeC is a non-wide-angle intraprediction mode;

Fig. 10 shows an example of the case where IntraPredModeC is derived from IntraPredModeY where IntraPredModeY is a non-wide-angle intraprediction mode and IntraPredModeC is a wide-angle intraprediction mode;

Fig. 11 shows an example of the case where IntraPredModeC is derived from IntraPredModeY using a prediction mode crop and where IntraPredModeY is a non-wide-angle intraprediction mode and IntraPredModeC is a non-wide-angle intraprediction mode;

Fig. 12A illustrates embodiments of a chroma component intra prediction block 1200 implemented in accordance with the present invention;

Fig. 12B illustrates embodiments of a chroma component intra prediction block 1210 implemented in accordance with the present invention;

Fig. 13 illustrates embodiments of a chroma component intra-prediction method 1300 implemented in accordance with the present invention;

Fig. 14 illustrates embodiments of a chroma component intra prediction device 1400 implemented in accordance with the present invention;

Fig. 15 is a block diagram showing an exemplary structure of a content delivery system 3100 that performs a content delivery service; and

Fig. 16 is a block diagram showing a structure of an example of a terminal device. In the following, identical reference signs refer to identical or at least functionally equivalent features unless otherwise explicitly specified.

Detailed description of the achievements

In the following description, reference is made to the accompanying figures, which form part of the description and which show, by way of illustration, specific aspects of embodiments of the invention or specific aspects in which embodiments of the present invention may be used. It is understood that embodiments of the invention may be used in other aspects and include structural or logical changes not shown in the figures. The following detailed description, therefore, should not be taken in a limiting sense, and the scope of the present invention is defined by the appended claims.

For example, it is understood that a description relating to a disclosed method may also apply to a corresponding device or system configured to perform the method and vice versa. For example, if one or a plurality of specific method steps are described, a corresponding device may include one or a plurality of units, e.g., functional units, for performing the one or plurality of described method steps (e.g., one unit performing the one or plurality of steps, or a plurality of units each performing one or more of the plurality of steps), even if such one or more units are not explicitly described or illustrated in the figures. On the other hand, for example, if a specific apparatus is described based on one or a plurality of units, e.g., functional units, a corresponding method may include a step for realizing the functionality of the one or a plurality of units (e.g., a step realizing the functionality of the one or a plurality of units, or a plurality of steps each of which realizing the functionality of one or more of the plurality of units), even if such one or the plurality of steps are not explicitly described or illustrated in the figures. Furthermore, it is understood that features of the various exemplary embodiments and/or aspects described herein may be combined with each other, unless specifically indicated otherwise.

Video coding generally refers to the processing of a sequence of images, which form the video or video sequence. Instead of the term “image”, the term “frame” or “picture” can be used as synonyms in the field of video coding. Video coding (or coding in general) comprises two parts of video encoding and decoding. Video encoding is performed at the source side, and typically comprises processing (e.g. by compression) of the original video images to reduce the amount of data required to represent the video images (for more efficient storage and/or transmission). Video decoding is performed at the destination side and typically comprises reverse processing compared to the encoder to reconstruct the video images. Embodiments referring to “encoding” of video images (or images in general) will be understood as relating to “encoding” or “decoding” of respective video images or video sequences. The combination of encoding part and decoding part is also known as CODEC (Encoding and Decoding).

In case of lossless video coding, the original video images can be reconstructed, i.e. the reconstructed video images have the same quality as the original video images (assuming no transmission loss or other data loss during storage or transmission). In case of lossy video coding, additional compression, e.g. by quantization, is used to reduce the amount of data representing the video images, which cannot be completely reconstructed in the decoder, i.e. the quality of the reconstructed video images is lower or worse compared to the quality of the original video images.

Several video coding standards belong to the group of “hybrid lossy video codecs” (i.e. they combine spatial and temporal prediction in the sample domain and 2D transform coding to apply quantization in the transform domain). Each frame in a video sequence is typically divided into a set of non-overlapping blocks and coding is typically performed at the block level. In other words, in the encoder, video is typically processed, i.e. encoded, at a block level (video block), for example by using spatial (intra-frame) prediction and/or temporal (inter-frame) prediction to generate a prediction block, subtracting the prediction block from the current block (currently processed/to-be-processed block) to obtain a residual block, transforming the residual block and quantizing the residual block in the transform domain to reduce the amount of data to be transmitted (compression), while in the decoder the inverse processing compared to the encoder is applied to the encoded or compressed block to reconstruct the current block for representation. Furthermore, the encoder duplicates the decoder's processing loop such that both will generate identical predictions (e.g., intra- and inter-predictions) and/or reconstructions to process, i.e., encode, subsequent blocks.

In the following embodiments of a video coding system 10, a video encoder 20 and a video decoder 30 are described based on Figs. 1 to 3.

Fig. 1A is a schematic block diagram illustrating an exemplary encoding system 10, e.g., a video encoding system 10 (or short encoding system 10) that may utilize techniques of this present application. The video encoder 20 (or short encoder 20) and the video decoder 30 (or short decoder 30) of the video coding system 10 represent examples of devices that may be configured to perform techniques according to various examples described in this application.

As shown in Fig. 1A, the encoding system 10 comprises a source device 12 configured to provide encoded image data 21, for example, to a destination device 14 for decoding the encoded image data 13.

The source device 12 comprises an encoder 20 and may further, i.e. optionally, comprise an image source 16, a preprocessor 18 (or preprocessing unit), for example an image preprocessor 18 and a communication interface or communication unit 22.

The image source 16 may comprise or be any type of image capture device, for example, a camera for capturing a real-world image, and/or any type of image generation device, for example, a computer graphics processor for generating a computer animated image, or any other device for obtaining and/or providing a real-world image, a computer generated image (e.g., a screen content, a virtual reality (VR) image), and/or any combination thereof (e.g., an augmented reality (AR) image). The image source may be any type of memory or storage that stores any of the aforementioned images.

Unlike the preprocessor 18 and the processing performed by the preprocessing unit 18, the image or image data 17 may also be referred to as a raw image or raw image data 17.

The preprocessor 18 is configured to receive the (raw) image data 17 and to perform preprocessing of the image data 17 to obtain a preprocessed image 19 or preprocessed image data 19. The preprocessing performed by the processor 18 may comprise, for example, cropping, color format conversion (e.g., from RGB to YCbCr), color correction, or noise removal. It can be understood that the preprocessing unit 18 may be an optional component.

The video encoder 20 is configured to receive the preprocessed image data 19 and provide encoded image data 21 (further details will be described below, e.g. based on FIG. 2). The communication interface 22 of the source device 12 may be configured to receive the encoded image data 21 and transmit the encoded image data 21 (or any further processed version thereof) via the communication channel 13 to another device, e.g., the destination device 14 or any other device, for storage or direct reconstruction.

The destination device 14 comprises a decoder 30 (for example, a video decoder 30), and may additionally comprise, i.e. optionally, a communication interface 28 or communication unit, a post-processor 32 (or post-processing unit 32) and a display device 34.

The communication interface 28 of the destination device 14 is configured to receive the encoded image data 21 (or any further processed version thereof), for example, directly from the source device 12 or from any other source, for example, a storage device, for example, an encoded image data storage device, and provide the encoded image data 21 to the decoder 30.

The communication interface 22 and the communication interface 28 may be configured to transmit or receive the encoded image data 21 or the encoded data 13 over a direct communication link between the source device 12 and the destination device 14, for example, a direct wired or wireless connection, or over any type of network, for example, a wired or wireless network or any combination thereof, or any type of public and private network, or any type of combination thereof.

The communication interface 22 may be configured, for example, to package the encoded image data 21 into an appropriate format, for example, packets, and/or process the encoded image data using any type of transmission encoding or processing for transmission over a communication link or communication network.

The communication interface 28, which forms the counterpart of the communication interface 22, may be configured, for example, to receive the transmitted data and process the transmission data using any corresponding type of transmission decoding or processing and/or unpacking to obtain the encoded image data 21.

Both the communication interface 22 and the communication interface 28 may be configured as one-way communication interfaces as indicated by the arrow for the communication channel 13 in Fig. 1A pointing from the source device 12 to the destination device 14, or two-way communication interfaces, and may be configured, for example, to send and receive messages, for example, to establish a connection, to acknowledge and exchange any other information related to the communication link and/or the transmission of data, for example, transmission of encoded image data.

The decoder 30 is configured to receive the encoded image data 21 and provide decoded image data 31 or a decoded image 31 (more details will be described below, for example, based on Fig. 3 or Fig. 5).

The post processor 32 of the destination device 14 is configured to further process the decoded image data 31 (also called reconstructed image data), e.g., the decoded image 31, to obtain post-processed image data 33, e.g., a post-processed image 33. The post-processing performed by the post-processing unit 32 may comprise, for example, color format conversion (e.g., from YCbCr to RGB), color correction, cropping or resampling, or any other processing, for example, to prepare the decoded image data 31 for display, e.g., by the display device 34.

The display device 34 of the target device 14 is configured to receive the post-processed image data 33 to display the image, for example, to a user or viewer. The display device 34 may be or comprise any type of display for representing the reconstructed image, for example, an integrated or external display device or monitor. The display devices may, for example, comprise liquid crystal displays (LCDs), organic light emitting diode displays (OLEDs), plasma displays, projectors, micro LED displays, liquid crystal on silicon (LCoS), digital light processor (DLP), or any other type of display.

Although FIG. 1A depicts the source device 12 and the destination device 14 as separate devices, embodiments of the devices may also comprise both or both of the source device 12 or corresponding functionality and the destination device 14 or corresponding functionality. In such embodiments, the source device 12 or corresponding functionality and the destination device 14 or corresponding functionality may be implemented using the same hardware and/or software or by separate hardware and/or software or any combination thereof.

As will be apparent to the skilled person based on the description, the (exact) existence and division of functionalities of the different units or functionalities within the source device 12 and/or the destination device 14 as shown in Fig. 1A may vary depending on the actual device and application.

The encoder 20 (e.g., a video encoder 20) or the decoder 30 (e.g., a video decoder 30) or both the encoder 20 and the decoder 30 may be implemented by processing circuitry as shown in FIG. 1B, such as one or more microprocessors, digital signal processors (DSPs), application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), discrete logic, hardware, dedicated video encoding, or any combination thereof. The encoder 20 may be implemented via processing circuitry 46 to incorporate the various modules as disclosed with respect to the encoder 20 of FIG. 2 and/or any other encoding system or subsystem described herein. The decoder 30 may be implemented via processing circuitry 46 to incorporate the various modules as disclosed with respect to the decoder 30 of FIG. 3 and/or any other decoder system or subsystem described herein. The processing circuitry may be configured to perform the various operations as disclosed below. As shown in FIG. 5, if the techniques are partially implemented in software, a device may store instructions for the software on a suitable, non-transitory, computer-readable storage medium and may execute the instructions in hardware using one or more processors to perform the techniques of this disclosure. Both the video encoder 20 and the video decoder 30 may be integrated as part of a combined encoder/decoder (CODEC) in a single device, for example, as shown in FIG. 1B.

The source device 12 and the destination device 14 may comprise any of a wide range of devices, including any type of handheld or stationary device, for example, laptop or notebook computers, mobile phones, smart phones, tablets, cameras, desktop computers, set-top boxes, televisions, display devices, digital media players, video game consoles, video streaming devices (such as content service servers or content delivery servers), broadcast receiver device, broadcast transmitter device, or the like and may not utilize any type of operating system. In some instances, the source device 12 and the destination device 14 may be equipped for wireless communication. Thus, the source device 12 and the destination device 14 may be wireless communication devices.

In some instances, the video encoding system 10 illustrated in FIG. 1A is merely an example and the techniques of the present application may be applied to video encoding configurations (e.g., video encoding or video decoding) that do not necessarily include any data communication between the encoding and decoding devices. In other examples, data is retrieved from a local memory, transmitted over a network, or the like. A video encoding device may encode and store data in memory and/or a video decoding device may retrieve and decode data from memory. In some examples, the encoding and decoding is performed by devices that do not communicate with each other, but simply encode data in memory and/or retrieve and decode data from memory.

For convenience of description, embodiments of the invention are described herein, for example, by reference to High Efficiency Video Coding (HEVC) or Versatile Video Coding (VVC) reference software, the next generation video coding standard developed by the Joint Collaboration Team on Video Coding (JCT-VC) of the ITU-T Video Coding Experts Group (VCEG) and the ISO/IEC Moving Picture Experts Group (MPEG). One skilled in the art will understand that embodiments of the invention are not limited to HEVC or VVC.

Encoder and Coding Method

[0031] FIG. 2 shows a schematic block diagram of an exemplary video encoder 20 that is configured to implement the techniques of the present application. In the example of FIG. 2 , the video encoder 20 comprises an input 201 (or input interface 201), a residual calculation unit 204, a transform processing unit 206, a quantization unit 208, an inverse quantization unit 210 and an inverse transform processing unit 212, a reconstruction unit 214, a loop filter unit 220, a decoded picture buffer (DPB) 230, a mode selection unit 260, an entropy encoding unit 270, and an output 272 (or output interface 272). The mode selection unit 260 may include an inter prediction unit 244, an intra prediction unit 254, and a partitioning unit 262. The inter prediction unit 244 may include a motion estimation unit and a motion compensation unit (not shown). A video encoder 20 as shown in FIG. 2 may also be referred to as a hybrid video encoder or a video encoder according to a hybrid video codec.

The residual calculation unit 204, the transform processing unit 206, the quantization unit 208, the mode selection unit 260 may be referred to as forming a forward signal path of the encoder 20, while the inverse quantization unit 210, the inverse transform processing unit 212, the reconstruction unit 214, the buffer 216, the loop filter 220, the decoded picture buffer (DPB) 230, the inter prediction unit 244 and the intra prediction unit 254 may be referred to as forming a backward signal path of the video encoder 20, wherein the backward signal path of the video encoder 20 corresponds to the signal path of the decoder (see video decoder 30 in FIG. 3). The inverse quantization unit 210, the inverse transform processing unit 212, the reconstruction unit 214, the loop filter 220, the decoded picture buffer (DPB) 230, the inter prediction unit 244 and the intra prediction unit 254 also refer to the formation of the “embedded decoder” of the video encoder 20.

Images and Image Partitioning (Images and Blocks)

The encoder 20 may be configured to receive, for example, via input 201, a picture 17 (or picture data 17), for example a picture from a sequence of pictures forming a video or video sequence. The received picture or picture data may also be a pre-processed picture 19 (or pre-processed picture data 19). For the sake of simplicity, the following description refers to picture 17. Picture 17 may also be referred to as current picture or picture to be encoded (in particular in video coding to distinguish the current picture from other, for example previously encoded pictures and/or decoded pictures of the same video sequence, i.e. the video sequence also comprising the current picture).

A (digital) image is or can be thought of as a two-dimensional grouping or array of samples with intensity values. A sample in the array may also be called a pixel (short for picture element) or a pel. The number of samples in the horizontal and vertical direction (or axis) of the array or image defines the size and/or resolution of the image. For color representation, typically three color components are used, i.e. the image can be represented or include three sample arrays. In RGB format or color space, an image comprises a corresponding red, green and blue sample array. However, in video coding, each pixel is typically represented in a luminance and chrominance format or color space, for example YCbCr, which comprises one luminance component denoted by Y (sometimes L is also used instead) and two chrominance components denoted by Cb and Cr. The luminance (or short luma) component Y represents the brightness or gray level intensity (e.g. as in a grayscale image), while the two chrominance (or short chrominance) components Cb and Cr represent the chromatic or color information components. Accordingly, an image in YCbCr format comprises a luminance sample array of luminance sample values (Y) and two chrominance sample arrays of chrominance values (Cb and Cr). Images in rG b format can be converted or transformed to YCbCr format and vice versa, the process is also known as color transformation or conversion. If an image is monochrome, the image may comprise only one luminance sample matrix. Thus, an image may be, for example, one luminance sample matrix in monochrome format or one luminance sample matrix and two corresponding chroma sample matrices in 4:2:0, 4:2:2 and 4:4:4 color format.

Embodiments of the video encoder 20 may comprise a picture partitioning unit (not shown in FIG. 2 ) configured to partition the picture 17 into a plurality of (typically non-overlapping) picture blocks 203. These blocks may also be referred to as root blocks, macroblocks (H.264/AVC), or coding tree blocks (CTB) or coding tree units (CTU) (H.265/HEVC and VVC). The picture partitioning unit may be configured to use the same block size for all pictures in a video sequence and a corresponding grid defining the block size, or to change the block size between pictures or subsets or groups of pictures, and to partition each picture into corresponding blocks.

In further embodiments, the video encoder may be configured to directly receive a block 203 of the image 17, for example, one, several, or all of the blocks that make up the image 17. The image block 203 may also be referred to as the current image block or the image block to be encoded.

Like image 17, image block 203 is again or can be considered as a two-dimensional array or matrix of samples with intensity values (sample values), although of lower dimension than image 17. In other words, block 203 may comprise, for example, one sample matrix (e.g., one luma matrix in the case of a monochrome image 17, or one luma or chroma matrix in the case of a color image) or three sample matrices (e.g., one luma and two chroma matrices in the case of a color image 17) or any other number and/or type of matrices according to the applied color format. The number of samples in the horizontal and vertical direction (or axis) of block 203 defines the size of block 203. Accordingly, a block may be, for example, an MxN sample matrix (M column by N row), or an MxN matrix of transform coefficients.

Embodiments of the video encoder 20 as shown in Fig. 2 may be configured to encode the image 17 block by block, for example, the encoding and prediction is performed per block 203.

Embodiments of the video encoder 20 as shown in FIG. 2 may be further configured to partition and/or encode the image using segments (also referred to as video segments), wherein an image may be partitioned or encoded using one or more (typically non-overlapping) segments, and each segment may comprise one or more blocks (e.g., CTUs).

Embodiments of the video encoder 20 as shown in FIG. 2 may be further configured to partition and/or encode the image using groups of tiles (also referred to as video tile groups) and/or tiles (also referred to as video tiles), wherein an image may be partitioned or encoded using one or more groups of tiles (typically non-overlapping), and each group of tiles may comprise, for example, one or more blocks (e.g., CTUs) or one or more tiles, wherein each tile, for example, may be rectangular in shape and may comprise one or more blocks (e.g., CTUs), for example, full or fractional blocks.

Residual Calculation

The residual calculation unit 204 may be configured to calculate a residual block 205 (also referred to as residual 205) based on the image block 203 and a prediction block 265 (more details on the prediction block 265 are provided below), for example, by subtracting sample values of the prediction block 265 from the sample values of the image block 203, sample by sample (pixel by pixel) to obtain the residual block 205 in the sample domain.

Transformed

The transform processing unit 206 may be configured to apply a transform, for example, a discrete cosine transform (DCT) or discrete sine transform (DST), on the sample values of the residual block 205 to obtain the transform coefficients 207 in a transform domain. The transform coefficients 207 may also be referred to as transform residual coefficients and represent the residual block 205 in the transform domain.

The transform processing unit 206 may be configured to apply integer approximations of DCT/DST, such as the transforms specified for H.265/HEVC. Compared to an orthogonal DCT transform, these integer approximations are typically scaled by a certain factor. To preserve the norm of the residual block being processed by forward and inverse transforms, additional scaling factors are applied as part of the transform process. The scaling factors are typically chosen based on certain constraints, such as scaling factors being a power of two for shift operations, bit depth of the transform coefficients, trade-off between accuracy and implementation costs, etc. Specific scale factors are specified, for example, for the inverse transform, for example by the inverse transform processing unit 212 (and the corresponding inverse transform, for example, by the inverse transform processing unit 312 in the video decoder 30) and corresponding scale factors for the forward transform, for example, by the transform processing unit 206, in an encoder 20 may be specified accordingly.

Embodiments of the video encoder 20 (respectively the transform processing unit 206) may be configured to output transform parameters, e.g., a type of transform or transforms, e.g., directly or encoded or compressed via the entropy encoding unit 270, such that, for example, the video decoder 30 may receive and use the transform parameters for decoding.

Quantification

The quantization unit 208 may be configured to quantize the transform coefficients 207 to obtain quantized coefficients 209, for example, by applying scalar quantization or vector quantization. The quantized coefficients 209 may also be referred to as quantized transform coefficients 209 or quantized residual coefficients 209.

The quantization process may reduce the bit depth associated with some or all of the transform coefficients 207. For example, an n-bit transform coefficient may be rounded down to an m-bit transform coefficient during quantization, where n is greater than m. The degree of quantization may be modified by adjusting a quantization parameter (QP). For example, for scalar quantization, different scales may be applied to achieve finer or coarser quantization. Smaller quantization step sizes correspond to finer quantization, while larger quantization step sizes correspond to coarser quantization. The applicable quantization step size may be indicated by a quantization parameter (QP). The quantization parameter may be, for example, an index to a predefined set of applicable quantization step sizes. For example, small quantization parameters may correspond to fine quantization (small quantization step sizes) and large quantization parameters may correspond to coarse quantization (large quantization step sizes) or vice versa. Quantization may include division by a quantization step size and corresponding and/or inverse dequantization, for example, by inverse quantization unit 210, may include multiplication by the quantization step size. Embodiments according to some standards, for example, HEVC, may be configured to use a quantization parameter to determine the quantization step size. Generally, the quantization step size may be calculated based on a quantization parameter using a fixed-point approximation of an equation that includes division. Additional scaling factors may be introduced for quantization and dequantization to restore the residual block norm, which could be modified due to the scaling used in the fixed-point approximation of the equation for the quantization step size and the quantization parameter. In an exemplary implementation, the inverse transform scaling and dequantization could be combined. Alternatively, custom quantization tables can be used and signaled from an encoder to a decoder, e.g. in a bitstream. Quantization is a lossy operation, where the loss increases with increasing quantization stage sizes.

Embodiments of the video encoder 20 (respectively the quantization unit 208) may be configured to output quantization parameters (QP), for example, directly or encoded by the entropy encoding unit 270, so that, for example, the video decoder 30 may receive and apply the quantization parameters for decoding.

Reverse Quantification

The inverse quantization unit 210 is configured to apply the inverse quantization of the quantization unit 208 on the quantized coefficients to obtain dequantized coefficients 211, for example, by applying the inverse of the quantization scheme applied by the quantization unit 208 based on or using the same quantization step size as the quantization unit 208. The dequantized coefficients 211 may also be referred to as dequantized residual coefficients 211 and correspond, although are typically not identical to the transform coefficients due to quantization loss, to the transform coefficients 207.

Inverse Transform

The inverse transform processing unit 212 is configured to apply the inverse transform of the transform applied by the transform processing unit 206, for example, an inverse discrete cosine transform (DCT) or an inverse discrete sine transform (DST) or other inverse transforms, to obtain a reconstructed residual block 213 (or the corresponding dequantized coefficients 213) in the sample domain. The reconstructed residual block 213 may also be referred to as a transform block 213.

Reconstruction

The reconstruction unit 214 (e.g., adder or summer 214) is configured to add the transform block 213 (i.e., the reconstructed residual block 213) to the prediction block 265 to obtain a reconstructed block 215 in the sample domain, for example, by adding, sample by sample, the sample values of the reconstructed residual block 213 and the sample values of the prediction block 265.

Filtration

The loop filter unit 220 (or “loop filter” 220 for short), is configured to filter the reconstructed block 215 to obtain a filtered block 221 or, in general, to filter reconstructed samples to obtain filtered samples. The loop filter unit is configured, for example, to smooth pixel transitions or otherwise improve video quality. The loop filter unit 220 may comprise one or more loop filters such as a deblocking filter, a sample adaptive shift (SAO) filter, or one or more other filters, for example, a bilateral filter, an adaptive loop filter (ALF), a sharpening filter, anti-aliasing filters, or collaborative filters, or any combination thereof. Although the loop filter unit 220 is shown in FIG. 2 as a loop filter, in other configurations, the loop filter unit 220 may be implemented as a post loop filter. Filtered block 221 may also be referred to as filtered reconstructed block 221.

Embodiments of the video encoder 20 (respectively the loop filter unit 220) may be configured to output loop filter parameters (such as sample adaptive shift information), for example, directly or encoded via the entropy encoding unit 270, so that, for example, a decoder 30 may receive and apply the same or respective loop filter parameters for decoding.

Decoded image buffer

The decoded picture buffer (DPB) 230 may be a memory that stores reference pictures, or generally reference picture data, for encoding video data by the video encoder 20. The DPB 230 may be formed by any of a variety of memory devices, such as dynamic random access memory (DRAM), including synchronous DRAM (SDRAM), magnetoresistive RAM (MRAM), resistive RAM (RRAM), or other types of memory devices. The decoded picture buffer (DPB) 230 may be configured to store one or more filtered blocks 221. The decoded image buffer 230 may be further configured to store other previously filtered blocks, e.g., previously reconstructed and filtered blocks 221, of the same current image or of different images, e.g., previously reconstructed images, and may provide complete previously reconstructed, i.e., decoded images (and corresponding reference blocks and samples) and/or a partially reconstructed current image (and corresponding reference blocks and samples), e.g., for inter prediction. The decoded image buffer (DPB) 230 may also be configured to store one or more unfiltered reconstructed blocks 215 or, in general, unfiltered reconstructed samples, e.g., if the reconstructed block 215 is not filtered by the loop filter unit 220, or any other further processed version of the reconstructed blocks or samples.

Mode selection (partitioning and prediction)

The mode selection unit 260 comprises the partitioning unit 262, the inter prediction unit 244 and the intra prediction unit 254, and is configured to receive or obtain original image data, for example, an original block 203 (current block 203 of the current image 17), and reconstructed image data, for example, filtered and/or unfiltered reconstructed samples or blocks of the same (current) image and/or of one or a plurality of previously decoded images, for example, from the decoded image buffer 230 or other buffers (e.g., line buffer, not shown). The reconstructed image data is used as reference image data for prediction, for example, inter prediction or intra prediction, to obtain a prediction block 265 or predictor 265.

The mode selection unit 260 may be configured to determine or select a partitioning for a current block prediction mode (which does not include partitioning) and a prediction mode (for example, an inter- or intra-prediction mode) and generate a corresponding prediction block 265, which is used for calculating the residual block 205 and reconstructing the reconstructed block 215.

Embodiments of the mode selection unit 260 may be configured to select the partitioning and prediction mode (e.g., from those supported by or available to the mode selection unit 260), which provide the best match, or in other words, minimum residue (minimum residue means better compression for transmission or storage), or minimum signaling overhead (minimum signaling overhead means better compression for transmission or storage), or which considers or balances both. The mode selection unit 260 may be configured to determine the partitioning and prediction mode based on rate distortion optimization (RDO), i.e., select the prediction mode which provides minimum rate distortion. Terms such as “best,” “minimum,” “optimal,” etc. In this context they do not necessarily refer to an overall “best”, “minimum”, “optimal”, etc., but may also refer to compliance with a selection criterion or criterion such as a value exceeding or falling below a threshold or other constraints potentially leading to a “suboptimal selection” but reducing complexity and processing time.

In other words, the partitioning unit 262 may be configured to partition the block 203 into smaller block or sub-block partitions (which again form blocks), for example, by iteratively using quaternary tree (QT) partitioning, binary partitioning (BT) or ternary tree (TT) partitioning or any combination thereof, and to perform, for example, prediction for each of the block or sub-block partitions, wherein the mode selection comprises selecting the tree structure of the partitioned block 203 and the prediction modes are applied to each of the block or sub-block partitions.

Next, the division (for example, by division unit 260) and prediction processing (by inter prediction unit 244 and intra prediction unit 254) performed by an example video encoder 20 will be explained in more detail.

Partitioning

The partitioning unit 262 can partition (or split) a current block 203 into smaller partitions, for example, smaller blocks of square or rectangular size. These smaller blocks (which may also be referred to as sub-blocks) can be further split into even smaller partitions. This also refers to tree partitioning or hierarchical tree partitioning, where a root block, for example, at root tree level 0 (hierarchy level 0, depth 0), can be recursively partitioned, for example, partitioned into two or more blocks of a next lower tree level, for example, nodes at tree level 1 (hierarchy level 1, depth 1), where these blocks can be further split into two or more blocks of a next lower level, for example, tree level 2 (hierarchy level 2, depth 2), etc. until partitioning is complete, for example because a termination criterion is met, such as a maximum tree depth or minimum block size is reached. Blocks that are not further partitioned are also called leaf blocks or leaf nodes of the tree. A tree that uses two-partition partitioning is called a binary tree (BT), a tree that uses three-partition partitioning is called a ternary tree (TT), and a tree that uses four-partition partitioning is called a quaternary tree (QT).

As mentioned above, the term “block” as used herein may be a portion, in particular a square or rectangular portion, of an image. With reference to, for example, HEVC and VVC, the block may be or correspond to a coding tree unit (CTU), a coding unit (CU), a prediction unit (PU) and a transform unit (TU) and/or corresponding blocks, for example, a coding tree block (CTB), a coding block (CB), a transform block (TB) or a prediction block (PB).

For example, a coding tree unit (CTU) may be or comprise a CTB of luma samples, two corresponding CTBs of chroma samples of an image having three sample arrays, or a CTB of samples of a monochrome image or an image that is encoded using three separate color planes and syntax structures used to encode the samples. Accordingly, a coding tree block (CTB) may be an NxN block of samples for some value of N, such that partitioning a component into CTBs is a partitioning. A coding unit (CU) may be or comprise a coding block of luma samples, two corresponding coding blocks of chroma samples of an image having three sample arrays, or a coding block of samples of a monochrome image or an image that is encoded using three separate color planes and syntax structures used to encode the samples. Correspondingly, a coding block (CB) can be an MxN block of samples for some values of M and N, such that dividing a CTB into coding blocks is a partitioning.

In embodiments, for example according to HEVC, a coding tree unit (CTU) may be split into CUs using a quaternary tree structure denoted as a coding tree. The decision to encode an image area using inter-picture (temporal) or intra-picture (spatial) prediction is made at the CU level. Each CU may be split into one, two or four PUs based on the PU split type. Within a PU, the same prediction process is applied and relevant information is transmitted to the decoder per PU. After obtaining the residual block by applying the prediction process based on the PU split type, a CU may be split into transform units (TUs) based on another quaternary tree structure similar to the coding tree of the CU.

In embodiments, for example, according to the latest video coding standard currently under development, which is called Versatile Video Coding (VVC), a combined quad-tree and binary tree (QTBT) partitioning is used to partition a coding block. In the QTBt block structure, a CU may be either square or rectangular in shape. For example, a coding tree unit (CTU) is first partitioned into a quad-tree structure. The quad-tree leaf nodes are further partitioned by a binary tree or a ternary (or triple) tree structure. The leaf nodes of the partitioning tree are called coding units (CU), and that segmentation is used for prediction and transform processing without further partitioning. This means that CU, PU and TU have the same block size in the QTBT coding block structure. In parallel, multiple partitioning, e.g. ternary tree partitioning can be used together with the QTBT block structure.

In one example, the mode selection unit 260 of the video encoder 20 may be configured to perform any combination of the partitioning techniques described herein.

As described above, the video encoder 20 is configured to determine or select the best or an optimal prediction mode from a set of (e.g., predetermined) prediction modes. The set of prediction modes may comprise, for example, intra-prediction modes and/or inter-prediction modes.

Intra prediction

The set of intra prediction modes may comprise 35 different intra prediction modes, for example non-directional modes such as DC (or half) mode and flat mode, or directional modes, for example as defined in HEVC, or it may comprise 67 different intra prediction modes, for example non-directional modes such as DC (or half) mode and flat mode, or directional modes, for example as defined for VVC.

The intra prediction unit 254 is configured to use reconstructed samples from contiguous blocks of the same current image to generate an intra prediction block 265 according to an intra prediction mode from the set of intra prediction modes.

The intra prediction unit 254 (or generally the mode selection unit 260) is further configured to send intra prediction parameters (or generally information indicative of the intra prediction mode selected for the block) to the entropy encoding unit 270 in the form of syntax elements 266 for inclusion in the encoded image data 21, so that, for example, the video decoder 30 can receive and use the prediction parameters for decoding.

Interprediction

The set of (or possible) inter-prediction modes depends on the available reference pictures (i.e., at least partially decoded previous pictures, e.g., stored in DBP 230) and other inter-prediction parameters, e.g., whether the entire reference picture or only a portion, e.g., a search window area around the current block area, of the reference picture is used to search for a best-matching reference block, and/or e.g., whether pixel interpolation, e.g., half-/semi-pel and/or quarter-pel interpolation, is applied or not.

In addition to the above prediction modes, jump mode and/or direct mode can be applied.

The inter-prediction unit 244 may include a motion estimation (ME) unit and a motion compensation (MC) unit (both not shown in FIG. 2 ). The motion estimation unit may be configured to receive or obtain the image block 203 (current image block 203 of the current image 17) and a decoded image 231, or at least one or a plurality of previously reconstructed blocks, e.g., reconstructed blocks from one or a plurality of other/different previously decoded images 231, for motion estimation. For example, a video sequence may comprise the current image and the previously decoded images 231, or, in other words, the current image and the previously decoded images 231 may be part of or form a sequence of images that form a video sequence.

The encoder 20 may, for example, be configured to select a reference block from a plurality of reference blocks of the same or different pictures from the plurality of other pictures and provide a reference picture (or reference picture index) and/or an offset (spatial displacement) between the position (x,y coordinates) of the reference block and the position of the current block as inter-prediction parameters for the motion estimation unit. This offset is also called a motion vector (MV).

The motion compensation unit is configured to obtain, for example, receive, an inter prediction parameter and perform an inter prediction based on or using the inter prediction parameter to obtain an inter prediction block 265. The motion compensation, performed by the motion compensation unit, may involve searching for or generating the prediction block based on the motion vector/block determined by motion estimation, possibly performing sub-pixel accurate interpolations. The interpolation filtering may generate additional pixel samples from known pixel samples, thereby potentially increasing the number of candidate prediction blocks that can be used to encode an image block. Upon receiving the motion vector for the current image block's PU, the motion compensation unit may locate the prediction block pointed to by the motion vector in one of the reference image lists.

The motion compensation unit may also generate syntax elements associated with the video blocks and segments for use by the video decoder 30 in decoding the image blocks of the video segment. In addition to, or as an alternative to, the segments and the respective syntax elements, tile groups and/or tiles and the respective syntax elements may be generated or used.

Entropy coding

The entropy coding unit 270 is configured to apply, for example, an entropy coding algorithm or scheme (e.g., a variable length coding (VLC) scheme, a context adaptive VLC (CAVLC) scheme, an arithmetic coding scheme, a binarization, a context adaptive binary arithmetic coding (CABAC), a syntax-based context adaptive binary arithmetic coding (SBAC), a probability interval partitioning entropy coding (PIPE), or other entropy coding methodology or technique) or derivation (without compression) on the quantized coefficients 209, inter prediction parameters, intra prediction parameters, loop filter parameters, and/or other syntax elements to obtain encoded image data 21 that can be output via the output 272, for example, in the form of an encoded bit stream 21, such that, for example, the video decoder 30 can receive and use the encoded image data 21. the parameters for decoding. The encoded bit stream 21 may be transmitted to the video decoder 30 or stored in a memory for later transmission or retrieval by the video decoder 30.

Other structural variations of the video encoder 20 may be used to encode the video stream. For example, a non-transform-based encoder 20 may quantize the residual signal directly without the transform processing unit 206 for certain blocks or frames. In another implementation, an encoder 20 may have the quantization unit 208 and the inverse quantization unit 210 combined into a single unit.

Decoder and Decoding Method

3 shows an example of a video decoder 30 that is configured to implement the techniques of this present application. The video decoder 30 is configured to receive encoded image data 21 (e.g., encoded bitstream 21), e.g., encoded by the encoder 20, to obtain a decoded image 331. The encoded image data or bitstream comprises information for decoding the encoded image data, e.g., data representing image blocks of an encoded video segment (and/or groups of tiles or mosaics) and associated syntax elements.

In the example of FIG. 3, the decoder 30 comprises an entropy decoding unit 304, an inverse quantization unit 310, an inverse transform processing unit 312, a reconstruction unit 314 (e.g., an adder 314), a loop filter 320, a decoded picture buffer (DBP) 330, a mode application unit 360, an inter prediction unit 344, and an intra prediction unit 354. The inter prediction unit 344 may be or include a motion compensation unit. The video decoder 30 may, in some examples, perform a decoding pass generally reciprocal to the encoding pass described with respect to the video encoder 100 of FIG. 2.

As explained with respect to the encoder 20, the inverse quantization unit 210, the inverse transform processing unit 212, the reconstruction unit 214, the loop filter 220, the decoded picture buffer (DPB) 230, the inter prediction unit 344, and the intra prediction unit 354 are also referred to as forming the “embedded decoder” of the video encoder 20. Accordingly, the inverse quantization unit 310 may be functionally identical to the inverse quantization unit 110, the inverse transform processing unit 312 may be functionally identical to the inverse transform processing unit 212, the reconstruction unit 314 may be functionally identical to the reconstruction unit 214, the loop filter 320 may be functionally identical to the loop filter 220, and the decoded picture buffer 230 may be functionally identical to the decoded picture buffer 230. Therefore, the explanations provided for the respective units and functions of the video encoder 20 correspondingly apply to the respective units and functions of the video decoder 30.

Decoding by Entropy

The entropy decoding unit 304 is configured to analyze the bit stream 21 (or generally encoded image data 21) and perform, for example, entropy decoding to the encoded image data 21 to obtain, for example, quantized coefficients 309 and/or decoded coding parameters (not shown in FIG. 3), for example, any or all of inter prediction parameters (e.g., reference picture motion vector and index), intra prediction parameter (e.g., intra prediction mode or index), transform parameters, quantization parameters, loop filter parameters, and/or other syntax elements. The entropy decoding unit 304 may be configured to apply decoding algorithms or schemes corresponding to the coding schemes described with respect to the entropy coding unit 270 of the encoder 20. The entropy decoding unit 304 may be further configured to provide inter prediction parameters, intra prediction parameters, and/or other syntax elements to the mode application unit 360 and other parameters to other units of the decoder 30. The video decoder 30 may receive the syntax elements at the video segment level and/or at the video block level. In addition to, or as an alternative to segments and the respective syntax elements, tile groups and/or tiles and the respective syntax elements may be received and/or used.

Reverse Quantification

The inverse quantization unit 310 may be configured to receive quantization parameters (QP) (or in general inverse quantization related information) and quantized coefficients of the encoded image data 21 (e.g., by analysis and/or decoding, e.g., by the entropy decoding unit 304) and to apply based on the quantization parameters, an inverse quantization on the decoded quantized coefficients 309 to obtain the dequantized coefficients 311, which may also be referred to as transform coefficients 311. The inverse quantization process may include using a quantization parameter determined by the video encoder 20 for each video block in the video segment (or tile or tile group) to determine a quantization degree and, likewise, a degree of inverse quantization that should be applied.

Inverse Transform

The inverse transform processing unit 312 may be configured to receive dequantized coefficients 311, also referred to as transform coefficients 311, and to apply a transform to the dequantized coefficients 311 to obtain reconstructed residual blocks 213 in the sample domain. The reconstructed residual blocks 213 may also be referred to as transform blocks 313. The transform may be an inverse transform, for example, an inverse DCT, an inverse DST, an inverse integer transform, or a conceptually similar inverse transform process. The inverse transform processing unit 312 may further be configured to receive transform parameters or corresponding information from the encoded image data 21 (e.g., by analyzing and/or decoding, for example, by the entropy decoding unit 30) to determine the transform to be applied to the dequantized coefficients 311.

Reconstruction

The reconstruction unit 314 (e.g., adder 314) may be configured to add the reconstructed residual block 313 to the prediction block 365 to obtain a reconstructed block 315 in the sample domain, for example, by adding the sample values of the reconstructed residual block 313 and the sample values of the prediction block 365.

Filtration

The in-loop filter unit 320 (either in the encoding loop or after the encoding loop) is configured to filter the reconstructed block 315 to obtain a filtered block 321, for example, to smooth pixel transitions or otherwise improve video quality. The in-loop filter unit 320 may comprise one or more in-loop filters such as a deblocking filter, a sample adaptive shift (SAO) filter, or one or more other filters, for example, a bilateral filter, an adaptive loop filter (ALF), a sharpening filter, a smoothing filter, or a collaborative filter, or any combination thereof. Although the in-loop filter unit 320 is shown in FIG. 3 as an in-loop filter, in other configurations, the in-loop filter unit 320 may be implemented as a post-loop filter.

Decoded image buffer

The decoded video blocks 321 of a picture are then stored in the decoded picture buffer 330, which stores the decoded pictures 331 as reference pictures for subsequent motion compensation for other pictures and/or for output display respectively.

The decoder 30 is configured to output the decoded image 311, for example, through the output 312, for presentation or display to a user.

Prediction

The inter prediction unit 344 may be identical to the inter prediction unit 244 (in particular the motion compensation unit) and the intra prediction unit 354 may be identical to the inter prediction unit 254 in function, and makes splitting or partitioning decisions and predictions based on the partitioning and/or prediction parameters or respective information received from the encoded image data 21 (e.g., by analysis and/or decoding, e.g., by the entropy decoding unit 304). The mode applying unit 360 may be configured to perform prediction (intra or inter prediction) on a block basis based on respective reconstructed images, blocks, or samples (filtered or unfiltered) to obtain the prediction block 365.

When the video segment is encoded as an intra coded (I) segment, the intra prediction unit 354 of the mode application unit 360 is configured to generate the prediction block 365 for a picture block of the current video segment based on a signaled intra prediction mode and previously decoded block data of the current picture. When the video picture is encoded as an inter coded (i.e., B or P) segment, the inter prediction unit 344 (e.g., motion compensation unit) of the mode application unit 360 is configured to produce prediction blocks 365 for a video block of the current video segment based on the motion vectors and other syntax elements received from the entropy decoding unit 304. For inter prediction, the prediction blocks may be produced from one of the reference pictures within one of the reference picture lists. The video decoder 30 may construct the reference frame lists, List 0 and List 1, using predetermined construction techniques based on reference pictures stored in DPB 330. The same or similar may be applied to or by embodiments using tile groups (e.g., video tile groups) and/or tiles (e.g., video tiles) in addition to or alternatively to segments (e.g., video segments), for example, a video may be encoded using tile groups and/or I, P, or B tiles.

The mode applying unit 360 is configured to determine prediction information for a video block of the current video segment by analyzing motion vectors or related information and other syntax elements, and uses the prediction information to produce prediction blocks for the current video block being decoded. For example, the mode applying unit 360 uses some of the received syntax elements to determine a prediction mode (e.g., intra- or inter-prediction) used to encode the video blocks of the video segment, an inter-prediction segment type (e.g., B segment, P segment, or GPB segment), construction information for one or more of the reference picture lists for the segment, motion vectors for each inter-coded video block of the segment, inter-prediction status for each inter-coded video block of the segment, and other information to decode the video blocks in the current video segment. The same or similar may apply to or by embodiments using groups of tiles (e.g., video tile groups) and/or tiles (e.g., video tiles) in addition to or alternatively to segments (e.g., video segments), for example, a video may be encoded using groups of tiles and/or I, P, or B tiles.

Embodiments of the video decoder 30 as shown in FIG. 3 may be configured to partition and/or decode the image using segments (also referred to as video segments), wherein an image may be partitioned or decoded using one or more (typically non-overlapping) segments, and each segment may comprise one or more blocks (e.g., CTUs).

Embodiments of the video decoder 30 as shown in FIG. 3 may be configured to partition and/or decode the image using groups of tiles (also referred to as video tile groups) and/or tiles (also referred to as video tiles), wherein an image may be partitioned or decoded using one or more groups of tiles (typically non-overlapping), and each group of tiles may comprise, for example, one or more blocks (e.g., CTUs) or one or more tiles, wherein each tile may, for example, be rectangular in shape and may comprise one or more blocks (e.g., CTUs), for example, whole blocks or in fractions.

Other variations of the video decoder 30 may be used to decode the encoded image data 21. For example, the decoder 30 may produce the output video stream without the loop filtering unit 320. For example, a transform-less decoder 30 may invert, quantize the residual signal directly without the inverse transform processing unit 312 for certain blocks or frames. In another implementation, the video decoder 30 may have the inverse quantization unit 310 and the inverse transform processing unit 312 combined into a single unit.

It should be understood that, in the encoder 20 and the decoder 30, a processing result of a current stage may be further processed and then sent to the next stage. For example, after interpolation filtering, motion vector derivation, or loop filtering, a further operation, such as cropping or shifting, may be performed on the processing result of the interpolation filtering, motion vector derivation, or loop filtering.

It should be noted that additional operations can be applied to motion vectors derived from the current block (including but not limited to affine mode pointwise motion vectors, affine, planar, ATMVP mode sub-block motion vectors, temporal motion vectors, etc.). For example, the value of the motion vector is restricted to a predefined range according to its representation bit. If the representation bit of the motion vector is bitDepth, then the range is -2A(bitDepth-1) ~ 2A(bitDepth-1)-1, where "A" means exponentiation. For example, if bitDepth is set to 16, the range is -32768 ~ 32767; If bitDepth is set to 18, the range is -131072~131071. For example, the value of the derived motion vector (e.g., the MVs of four 4x4 sub-blocks within an 8x8 block) is restricted such that the maximum difference between the integer parts of the four 4x4 sub-blocks MVs is no more than N pixels, such as no more than 1 pixel. Two methods are provided here to restrict the motion vector according to the bitDepth.

Method 1: Remove the leftover MSB (most significant bit) using stream operations

ux= (mvx+2bitDepth) % 2bitDepth (1)

mvx = (ux >= 2bitDepth-1) ? (ux - 2bitDepth) : ux (2)

uy= (mvy+2bitDepth) % 2bitDepth (3)

mvy = (oops >= 2bitDepth-1) ? (oops - 2bitDepth) : oops (4)

where mvx is a horizontal component of a motion vector of a block or an image sub-block, mvy is a vertical component of a motion vector of a block or an image sub-block, and ux and uy indicate an intermediate value;

For example, if the value of mvx is -32769, then after applying formula (1) and (2), the resulting value is 32767. In computer system, decimal numbers are stored as two's complement. The two's complement of -32769 is 1,0111,1111,1111,1111 (17 bits), then MSB is discarded, so the resulting two's complement is 0111,1111,1111,1111 (decimal number is 32767), which is the same as output by applying formula (1) and (2).

ux= (mvpx mvdx 2bitDepth) % 2bitDepth (5)

mvx = (ux >= 2bitDepth-1) ? (ux - 2bitDepth) : ux (6)

uy= (mvpy mvdy 2bitDepth) % 2bitDepth (7)

mvy = (oops >= 2bitDepth-1) ? (oops - 2bitDepth) : oops (8)

The operations can be applied during the addition of mvp and mvd, as shown in formula (5) to (8). Method 2: Remove the excess MSB by trimming the value

vx = Clip3(-2bitDepth_1, 2bitDepth'1 -1, vx)

vy = Clip3(-2bitDepth_1, 2bitDepth'1 -1, vy)

where vx is a horizontal component of a motion vector of an image block or sub-block, vy is a vertical component of a motion vector of an image block or sub-block; x, y, and z respectively correspond to three input values of the MV clipping process, and the definition of the Clip3 function is as follows:

x ; z < x

and ; z > y

Clip3(x, y, z) = <z otherwise>

Fig. 4 is a schematic diagram of a video encoding device 400 according to one embodiment of the disclosure. The video encoding device 400 is suitable for implementing the disclosed embodiments as described herein. In one embodiment, the video encoding device 400 may be a decoder such as the video decoder 30 of Fig. 1A or an encoder, such as the video encoder 20 of Fig. 1A.

The video encoding device 400 comprises access ports 410 (or input ports 410) and receiver (Rx) units 420 for receiving data; a processor, logic unit, or central processing unit (CPU) 430 for processing the data; transmitter (Tx) units 440 and output ports 450 (or output ports 450) for transmitting the data; and a memory 460 for storing the data. The video encoding device 400 may also comprise optical-to-electrical (OE) components and electrical-to-optical (EO) components coupled to the access ports 410, receiver units 420, transmitter units 440, and output ports 450 for outputting or inputting optical or electrical signals.

The processor 430 is implemented by hardware and software. The processor 430 may be implemented as one or more CPU chips, cores (e.g., as a multi-core processor), FPGA, ASIC, and DSP. The processor 430 is in communication with access ports 410, receiver units 420, transmitter units 440, output ports 450, and memory 460. The processor 430 comprises an encoding module 470. The encoding module 470 implements the embodiments described above. For example, the encoding module 470 implements, processes, prepares, or provides the various encoding operations. Thus, the inclusion of the encoding module 470 provides a substantial enhancement to the functionality of the video encoding device 400 and effects a transformation of the video encoding device 400 to a different state. Alternatively, the encoding module 470 is implemented as instructions stored in memory 460 and executed by processor 430.

Memory 460 may comprise one or more disk drives, tape drives, and solid state drives and may be used as a spare data storage device, for storing programs when such programs are selected for execution, and for storing instructions and data that are read during program execution. Memory 460 may be, for example, volatile and/or nonvolatile and may be read-only memory (ROM), random access memory (RAM), ternary content addressable memory (TCAM), and/or static random access memory (SRAM).

Fig. 5 is a simplified block diagram of an apparatus 500 that may be used as one or both of the source device 12 and the destination device 14 of Fig. 1 in accordance with an exemplary embodiment.

A processor 502 in apparatus 500 may be a central processing unit. Alternatively, processor 502 may be any other type of device, or multiple devices, capable of manipulating or processing information now existing or developed in the future. Although the disclosed implementations may be implemented with a single processor as shown, for example, processor 502, advantages in speed and efficiency may be achieved by using more than one processor.

A memory 504 in the apparatus 500 may be a read-only memory (ROM) device or a random access memory (RAM) device in one implementation. Any other suitable type of storage device may be used as memory 504. The memory 504 may include code and data 506 that is accessed by the processor 502 using a bus 512. The memory 504 may further include an operating system 508 and application programs 510, the application programs 510 including at least one program that enables the processor 502 to perform the methods described herein. For example, the application programs 510 may include applications 1 through N, further including a video encoding application that performs the methods described herein.

The apparatus 500 may also include one or more output devices, such as a display device 518. The display device 518 may be, in one example, a touch-sensitive display device that combines a display device with a touch-sensitive element that is operable to detect touch inputs. The display device 518 may be coupled to the processor 502 via bus 512.

Although shown here as a single bus, the bus 512 of the apparatus 500 may be comprised of multiple buses. In addition, the secondary storage 514 may be directly coupled to the other components of the apparatus 500 or may be accessed over a network and may comprise a single integrated unit such as a memory card or multiple units such as multiple memory cards. Thus, the apparatus 500 may be implemented in a wide variety of configurations.

Directional intraprediction is a well-known technique that involves propagating the values of neighboring samples in the predicted block as specified by the prediction direction. Fig. 6 illustrates the 93 prediction directions, where the dashed directions are associated with wide-angle modes that only apply to non-square blocks.

The direction could be specified by increasing an offset between the predicted sample position and the reference position. The larger magnitude of this increase corresponds to a larger bias of the prediction direction. Table 1 specifies the mapping table between predModeIntra and the angle parameter intraPredAngle. This parameter is in fact the increase of this offset per row (or per column) specified at the sample resolution 1/32.

Table 1 - intraPredAngle specification

Wide-angle modes can be identified by the absolute value of intraPredAngle greater than 32 (1 sample), which corresponds to the slope of the prediction direction greater than 45 degrees.

Predicted samples (“predSamples”) can be obtained from the neighboring samples “p” as described below:

The values of the prediction samples predSamples[x][y], with x = 0..nTbW - 1, y = 0..nTbH - 1 are derived as follows:

- If predModeIntra is greater than or equal to 34, the following ordered stages apply:

1. The reference sample array ref[x] is specified as follows:

- The following applies:

ref[x] = p[-1 - refIdx x][-1 - refIdx], with x = 0..nTbW refIdx

- If intraPredAngle is less than 0, the main reference sample array is extended as follows: - When (nTbH * intraPredAngle) >> 5 is less than -1,

ref[x] = p[-1 - refIdx][-1 - refIdx ((x * invAngle 128) >> 8)],

with x = -1..(nTbH * intraPredAngle) >> 5

ref[((nTbH * intraPredAngle) >> 5) - 1] = ref[(nTbH * intraPredAngle) >> 5]

ref[nTbW 1 refIdx] = ref[nTbW refIdx]

- Otherwise,

ref[x] = p[-1 - refIdx x][-1 - refIdx], with x = nTbW 1 refIdx..refW refIdx

ref[-1] = ref[0]

- The additional samples ref[refW refldx x] with x = 1..(Max(1, nTbW/nTbH) * refldx 1) are derived as follows:

ref[refW refIdx x] = p[-1 refW][-1 - refIdx]

2. The values of the prediction samples predSamples[x][y], with x = 0..nTbW - 1, y = 0..nTbH - 1 are derived as follows:

- The index variable iIdx and the multiplication factor iFact are derived as follows:

iIdx = ((y 1 refIdx) * intraPredAngle) >> 5 refIdx

iFact = ((y 1 refIdx) * intraPredAngle) & 31

- If cIdx is equal to 0, the following applies:

- The interpolation filter coefficients fT[j] with j = 0..3 are derived as follows:

fT[j] = filterFlag ? fG[iFact][j] : fC[iFact][j]

- The value of the prediction samples predSamples[x][y] is derived as follows:

predSamples[x][y] = C lip1Y(((£f=gfT[i ] * r e f [ s ildx-H i ]) 32) » 6)

- Otherwise (cIdx is not equal to 0), depending on the value of iFact, the following applies:

- If iFact is not equal to 0, the value of the prediction samples predSamples[x][y] is derived as follows: predSamples[x][y] =

((32 - iFact) * ref[x iIdx 1] iFact * ref[x iIdx 2] 16) >> 5

- Otherwise, the value of the prediction samples predSamples[x][y] is derived as follows: predSamples[x][y] = ref[x iIdx 1]

- Otherwise (predModeIntra is less than 34), the following ordered stages apply:

1. The reference sample array ref[x] is specified as follows:

- The following applies:

ref[x] = p[-1 - refIdx][-1 - refIdx x], with x = 0..nTbH refIdx

- If intraPredAngle is less than 0, the main reference sample array is extended as follows: - When (nTbW * intraPredAngle) >> 5 is less than -1,

ref[x] = p[-1 - refIdx ((x * invAngle 128) >> 8)][-1 - refIdx],

with x = -1..(nTbW * intraPredAngle) >> 5

ref[((nTbW * intraPredAngle) >> 5) - 1] =

ref[(nTbW * intraPredAngle) >> 5] (8-145)

ref[nTbG 1 refIdx] = ref[nTbH refIdx]

- Otherwise,

ref[x] = p[-1 - refIdx][-1 - refIdx x], with x = nTbH 1 refIdx..refH refIdx

ref[-1] = ref[0]

- The additional samples ref[refH refldx x] with x = 1..(Max(1, nTbW/nTbH) * refldx 1) are derived as follows:

ref[refH refIdx x] = p[-1 refH][-1 - refIdx]

2. The values of the prediction samples predSamples[x][y], with x = 0..nTbW - 1, y = 0..nTbH - 1 are derived as follows:

- The index variable iIdx and the multiplication factor iFact are derived as follows:

iIdx = ((x 1 refIdx) * intraPredAngle) >> 5

iFact = ((x 1 refIdx) * intraPredAngle) & 31

- If cIdx is equal to 0, the following applies:

- The interpolation filter coefficients fT[j] with j = 0..3 are derived as follows:

fT[j] = filterFlag ? fG[iFact][j] : fC[iFact][j]

- The value of the prediction samples predSamples[x][y] is derived as follows:

predSamples[x][y] = CMp1Y(((2f=afT [ i ] * re f[> ild x-H i ]) 32) » 6)

- Otherwise (cIdx is not equal to 0), depending on the value of iFact, the following applies:

- If iFact is not equal to 0, the value of the prediction samples predSamples[x][y] is derived as follows: predSamples[x][y] =

((32 - iFact) * ref[y iIdx 1] iFact * ref[y iIdx 2] 16) >> 5

- Otherwise, the value of the prediction samples predSamples[x][y] is derived as follows: predSamples[x][y] = ref[y iIdx 1]

The signaling of the intraprediction modes for the luma and chroma components could be done in such a way that the chroma intraprediction mode is derived from the luma intraprediction mode:

The chroma intraprediction mode IntraPredModeC[xCb ][ yCb ] is derived using intra_chroma_pred_mode[ xCb ][ yCb ] and IntraPredModeY[ xCb cbWidth / 2 ][ yCb cbHeight / 2 ] as specified in Table 2 and Table 3 .

Table 2 - IntraPredModeC[xCb][yCb] specification depending on intra_chroma_pred_mode[xCb][yCb] and IntraPredModeY[xCb cbWidth/2][yCb cbHeight/2] when sps_cclm_enabled_flag is equal to 0

Table 3 - IntraPredModeC[xCb][yCb] specification depending on intra_chroma_pred_mode[xCb][yCb] and IntraPredModeY[xCb cbWidth/2][yCb cbHeight/2] when sps_cclm_enabled_flag is equal to 1

The parameter “intra_chroma_pred_mode” is signaled within a bitstream. From Table 2 and Table 3 it can be observed that in certain cases (indicated by “X ”), the intra prediction mode for the chroma component (IntraPredModeC) is set equal to the intra prediction mode specified for the simultaneously located luma block.

The chroma format determines the precedence and subsampling of the chroma matrices, as shown in Fig. 7. In monochrome sampling, there is only one sample matrix, which is nominally considered the luma matrix.

In 4:2:0 sampling, each of the two chroma matrices is half the height and half the width of the luma matrix.

In 4:2:2 sampling, each of the two chroma matrices has the same height and is half the width of the luma matrix.

This solution provides the same intra prediction direction for predicting chrominance samples as is specified for luma samples. However, when the chroma subsampling ratio in horizontal direction is not equal to the chroma subsampling ratio in vertical direction, the intra prediction directions for chroma will be affected by subsampling, resulting in a different mapping of the intra prediction mode to the angle of the intra prediction direction. To compensate for this effect, it has been proposed in HM range extensions to perform a mode mapping step, i.e. to perform a lookup of the dedicated look-up table (LUT) for the corresponding luma intra prediction mode (IntraPredModeY) and use the lookup value for the chroma intra prediction mode (IntraPredModeC). Table 4 provides this LUT for the set of modes specified in the HEVC standard.

Table 4 - LUT specification for intra prediction mode assignment for 4:2:2 chroma format

In draft 4 of the VVC specification in the intra prediction process, the intra prediction mode index (intraPredMode) is modified according to the aspect ratio as follows:

The variables nW and nH are derived as follows:

- If IntraSubPartitionsSplitType is equal to ISP_N OR _SPLIT or cIdx is not equal to 0, the following applies: nW = nTbW

nH = nTbH

- Otherwise (IntraSubPartitionsSplitType is not equal to ISP_N OR _SPLIT and cldx is equal to 0), the following applies:

nW = nCbW

nH = nCbH

The variable whRatio is set equal to Abs(Log2(nW/nH)).

The wideAngle variable is set equal to 0.

For non-square blocks (nW is not equal to nH), the intra prediction mode predModeIntra is modified as follows:

- If all of the following conditions are true, wideAngle is set equal to 1 and predModeIntra is set equal to (predModeIntra 65).

- nW is greater than nH

- predModeIntra is greater than or equal to 2

- predModeIntra is less than (whRatio > 1) ? (8 2 * whRatio) : 8

- Otherwise, if all of the following conditions are true, wideAngle is set equal to 1 and predModeIntra is set equal to (predModeIntra - 67).

- nH is greater than nW

- predModeIntra is less than or equal to 66

- predModeIntra is greater than (whRatio > 1) ? (60 - 2 * whRatio) : 60

The process of modifying the intra prediction mode (predModeIntra) with respect to the aspect ratio (whRatio) described above would also be called “wide angle mapping”.

If the state-of-the-art approach is applied, the intra prediction direction for chroma samples may be opposite to the direction specified for simultaneously located luma samples, because the conditions for luma and chroma blocks would be different due to horizontal chroma subsampling as specified for YUV 4:2:2 chroma format. Embodiments of the invention propose to jointly consider the block aspect ratio and the chroma subsampling format when using the luma intra prediction mode for chroma intra prediction.

This description provides several methods to solve this problem. One method introduces the cropping operation to ensure that the directional intra prediction of luma and chroma uses the same side of the block. Another method involves modifying the wide angle assignment process to ensure that the resulting chroma prediction mode has the same angle of the assigned direction. As can be seen from the above description, these directions do not match. (“(PredModeIntra - 67)” and “(predModeIntra 65)”).

The third method according to embodiments of this invention includes adjusting the input parameters for the wide angle mapping process. Specifically, it is proposed to use a luma aspect ratio instead of a chroma aspect ratio. In addition, the intraPredAngle parameter is shifted left or right to compensate for the effect of chroma subsampling.

Alternatively, for the set of signaled luma intraprediction modes given in the draft VVC specification (which are in the range 0..66), the following lookup table (Table 5) could be used.

One of the possible solutions includes applying the LUT specified in Table 5 to the luma intraprediction mode value (IntraPredModeY) and using the obtained mode as an input intraprediction mode (IntraPredModeC) of the directional intraprediction process for the chroma block, which comprises:

- IntraPredModeC wide angle assignment

- derivation of the reference sample matrix (“ref”) and the intraPredAngle parameter

- obtaining the values of the predicted chroma samples using previously determined reference samples (“ref”) and the intraPredAngle parameter.

This approach works well if the luma intra prediction mode (IntraPredModeY) is not a wide angle mode. As shown in Fig. 9, the chroma and luma samples predicted at the same spatial positions “A” would use reference samples which are also at the same spatial positions. This method also works in the case shown in Fig. 11, because it specifies clipping the output chroma intra prediction direction at the angle of 45 degrees (mode 2). This clipping is implemented by specifying the same value for a set of inputs in the LUT (please note the entries IntraPredModeY = 2.. 8).

Another embodiment of the invention includes modifying the wide angle allocation process for the case where the “IntraPredModeC wide angle allocation” step is performed.

The following description specifies the additional dependency of the wide angle mapping process on whether the mapped direction is performed for chroma intra prediction for the chroma format by specifying different subsampling ratios in horizontal and vertical directions (further indicated as “SubWidthC” and “SubHeightC”, respectively):

The variables nW and nH are derived as follows:

- If IntraSubPartitionsSplitType is equal to ISP_N OR _SPLIT or cIdx is not equal to 0, the following applies: nW = nTbW

nH = nTbH

- Otherwise (IntraSubPartitionsSplitType is not equal to ISP_N OR _SPLIT and cIdx is equal to 0), the following applies:

nW = nCbW

nH = nCbH

If SubWidthC is not equal to SubHeightC, the value of the variable modeDelta is set to (cIdx==0?0:1), otherwise modeDelta is set to 0.

The variable whRatio is set equal to Abs(Log2(nW/nH)).

The wideAngle variable is set equal to 0.

For non-square blocks (nW is not equal to nH), the intra prediction mode predModeIntra is modified as follows:

- If all of the following conditions are true, wideAngle is set equal to 1 and predModeIntra is set equal to (predModeIntra 65 modeDelta).

- nW is greater than nH

- predModeIntra is greater than or equal to 2

- predModeIntra is less than (whRatio > 1) ? (8 2 * whRatio) : 8

- Otherwise, if all of the following conditions are true, wideAngle is set equal to 1 and predModeIntra is set equal to (predModeIntra - 67 modeDelta).

- nH is greater than nW

- predModeIntra is less than or equal to 66

- predModeIntra is greater than (whRatio > 1) ? (60 - 2 * whRatio) : 60

However, the above-described approaches may result in opposite directions of the luma and chroma intraprediction modes in case the luma intraprediction mode (IntraPredModeY) corresponds to the wide-angle direction. Fig. 8 shows an example of the case where IntraPredModeC is derived from IntraPredModeY where IntraPredModeY is a wide-angle intraprediction mode and IntraPredModeC is a non-wide-angle intraprediction mode. The example of the case where the expected intraprediction mode (as shown in Fig. 8) is not produced by the above-disclosed method. Fig. 9 shows an example of the case where IntraPredModeC is derived from IntraPredModeY where IntraPredModeY is a non-wide-angle intraprediction mode and IntraPredModeC is a non-wide-angle intraprediction mode. Fig. 10 shows an example of the case where IntraPredModeC is derived from IntraPredModeY where IntraPredModeY is a non-wide-angle intraprediction mode and IntraPredModeC is a wide-angle intraprediction mode. The example of the case (as shown in Fig. 10) when the input luma intraprediction mode without wide-angle (IntraPredModeY) produces the wide-angle chroma intraprediction mode (IntraPredModeC). Fig. 11 shows an example of the case where IntraPredModeC is derived from IntraPredModeY using prediction mode clipping and where IntraPredModeY is a non-wide-angle intraprediction mode and IntraPredModeC is a non-wide-angle intraprediction mode.

- An exemplary embodiment specifying the method (“Method 3”) shown in Fig. 8 and Fig. 10 could be described as the following steps when the chroma format is defined as YUV 4:2:2 and the input luma intra prediction mode (IntraPredModeY) is directional (i.e. not equal to DC and not equal to a PLANE): wide angle mapping (IntraPredModeY) using the aspect ratio of a luma block resulting in IntraPredModeFinalY;

- derivation of the reference sample matrix (“ref”) and the intraPredAngle parameter for the chroma block using the input prediction mode IntraPredModeFinalY, which comprises the following steps:

- in case IntraPredModeFinalY is not less than 34, the intraPredAngle parameter is redefined as follows:

intraPredAngle = intraPredAngle >>1

- otherwise the intraPredAngle parameter is redefined as follows

intraPredAngle = intraPredAngle <<1

- obtaining the values of predicted chroma samples using previously determined reference samples (“ref”) and the intraPredAngle parameter.

Alternatively, instead of the operation “intraPredAngle = intraPredAngle >>1” another implementation of division by 2 can be used, such as: “intraPredAngle = sign(intraPredAngle) * ((Abs(intraPredAngle)+1) >>1)” or “intraPredAngle = intraPredAngle/2”.

A combination of both methods could also be applied. One embodiment would comprise the following steps for an input luma intraprediction mode (IntraPredModeY) that is directional (i.e. not equal to DC and not equal to a PLANE):

- if IntraPredModeY is not less than 18 nor more than 50, the following steps apply

or obtaining the LUT (e.g. as specified in Table 5) using the luma intra prediction mode (IntraPredModeY) key value which results in the chroma input intra prediction mode (IntraPredModeC)

or IntraPredModeC wide angle assignment

or derivation of the reference sample matrix (“ref”) and the intraPredAngle parameter

or obtaining the values of the predicted chroma samples using previously determined reference samples (“ref”) and the intraPredAngle parameter.

- Otherwise, perform the steps specified in the description of “Method 3”.

An embodiment of the invention could also be represented as follows:

8.4.3 Derivation process for chroma intra prediction mode

The inputs to this process are:

- a luma location (xCb, yCb) that specifies the top-left sample of the current chroma encoding block relative to the top-left luma sample of the current image,

- a cbWidth variable specifying the width of the current coding block in luma samples, - a cbHeight variable specifying the height of the current coding block in luma samples. In this process, the chroma intra prediction mode IntraPredModeC[xCb][yCb] is derived.

The chroma intraprediction mode IntraPredModeC[xCb][yCb] is derived using intra_chroma_pred_mode[xCb][yCb] and IntraPredModeY[xCb cbWidth/2][yCb cbHeight/2] as specified in Table 8-2 and Table 8-3.

The chroma intra prediction mode IntraPredModeC[xCb][yCb] is derived using the map422 process.

Table 8-2 - IntraPredModeC[xCb][yCb] specification depending on intra_chroma_pred_mode[xCb][yCb] and IntraPredModeY[xCb cbWidth/2][yCb cbHeight/2] when sps_cclm_enabled_flag equals 0

Table 8-3 - IntraPredModeC[xCb][yCb] specification depending on intra_chroma_pred_mode[xCb][yCb] and IntraPredModeY[xCb cbWidth/2][yCb cbHeight/2] when sps_cclm_enabled_flag equals 1

In the mapping process, map422() of output intra prediction mode Y is derived from input intra prediction mode X as follows:

- The output intraprediction mode Y is set equal to the input intraprediction mode X if one of the following conditions is true:

- SubWidthC is equal to SubHeightC,

- X is less than 2,

- X is greater than 66

- Otherwise, the intraprediction mode Y is set equal to the value according to the lookup table defined in Table 8-4.

Table 8-4 - Lookup table specification for the 422 map assignment process ()

Another embodiment of the invention could also be represented as follows:

8.4.3 Derivation process for chroma intra prediction mode

The inputs to this process are:

- a luma location (xCb, yCb) that specifies the top-left sample of the current chroma encoding block relative to the top-left luma sample of the current image,

- a cbWidth variable specifying the width of the current coding block in luma samples, - a cbHeight variable specifying the height of the current coding block in luma samples. In this process, the chroma intra prediction mode IntraPredModeC[xCb][yCb] is derived.

The chroma intraprediction mode IntraPredModeC[xCb][yCb] is derived using intra_chroma_pred_mode[xCb][yCb] and IntraPredModeY[xCb cbWidth/2][yCb cbHeight/2] as specified in Table 8-2 and Table 8-3.

The chroma intra prediction mode IntraPredModeC[xCb][yCb] is derived using the map422 process.

Table 8-2 - IntraPredModeC[xCb][yCb] specification depending on intra_chroma_pred_mode[xCb][yCb] and IntraPredModeY[xCb+ cbWidth/2][yCb cbHeight/2] when sps_cclm_enabled_flag equals 0

Table 8-3 - IntraPredModeC[xCb][yCb] specification depending on intra_chroma_pred_mode[xCb][yCb] and IntraPredModeY[xCb cbWidth/2][yCb cbHeight/2] when sps_cclm_enabled_flag equals 1

In the mapping process, map422() of output intra prediction mode Y is derived from input intra prediction mode X as follows:

- The output intraprediction mode Y is set equal to an input intraprediction mode X if one of the following conditions is true:

- SubWidthC is equal to SubHeightC,

- X is less than 2,

- X is greater than 66

- Otherwise, the intraprediction mode Y is set equal to the value according to the lookup table defined in Table 8-4.

The variable nW is set equal to cbWidth, the variable nH is set equal to cbHeight. The variable whRatio is set equal to Abs(Log2(nW/nH)).

For non-square blocks (nW is not equal to nH), the output intraprediction mode Y clipping is performed as follows:

- If all of the following conditions are true, Y is set equal to ((whRatio > 1) ? (8 2 * whRatio) : 8):

- nW is greater than nH

- And it is greater than or equal to 2

- And is it less than (whRatio > 1) ? (8 2 * whRatio) : 8

- Otherwise, if all of the following conditions are true, AND is set equal to ((whRatio > 1) ? (60 - 2 * whRatio) : 60):

- nH is greater than nW

- And it is less than or equal to 66

- And is it greater than (whRatio > 1) ? (60 - 2 * whRatio) : 60

Table 8-4 - Lookup table specification for the 422() map assignment process

A method for setting the intraPredAngle parameter could also be implemented as follows:

8.4.4.2.7Specification of intra-prediction modes INTRA_ANGULAR2..INTRA_ANGULAR66

The inputs to this process are:

- the intraprediction mode predModeIntra,

- a refIdx variable specifying the index of the intraprediction reference line,

- an nTbW variable specifying the width of the transform block,

- a nTbH variable specifying the height of the transform block,

- a refW variable specifying the width of the reference samples,

- a refH variable specifying the height of the reference samples,

- an nCbW variable specifying the width of the coding block,

- an nCbH variable specifying the height of the coding block,

- a cIdx variable that specifies the color component of the current block,

- the adjacent samples p[x][y], with x = -1 - refIdx, y = -1 - refIdx..refH - 1 and x = -refIdx..refW - 1, y = -1 -refIdx.

The outputs of this process are the modified intra prediction mode predModeIntra and the predicted samples predSamples[x][y], with x = 0..nTbW - 1, y = 0..nTbH - 1.

The variable nTbS is set equal to (Log2(nTbW) Log2(nTbH)) >> 1.

The variables nW and nH are derived as follows:

- If IntraSubPartitionsSplitType is equal to ISP_N OR _SPLIT or cIdx is not equal to 0, the following applies: nW = nTbW

nH = nTbH

- Otherwise (IntraSubPartitionsSplitType is not equal to ISP_N OR _SPLIT and cldx is equal to 0), the following applies:

nW = nCbW

nH = nCbH

The variable whRatio is set equal to Abs(Log2(nW/nH)).

If cIdx is not equal to 0 and subWidthC is greater than subHeightC, whRatio is incremented by 1.

The wideAngle variable is set equal to 0.

For non-square blocks (nW is not equal to nH), the intra prediction mode predModeIntra is modified as follows:

- If all of the following conditions are true, wideAngle is set equal to 1 and predModeIntra is set equal to (predModeIntra 65).

- nW is greater than nH

- predModeIntra is greater than or equal to 2

- predModeIntra is less than (whRatio > 1) ? (8 2 * whRatio) : 8

- Otherwise, if all of the following conditions are true, wideAngle is set equal to 1 and predModeIntra is set equal to (predModeIntra - 67).

- nH is greater than nW

- predModeIntra is less than or equal to 66

- predModeIntra is greater than (whRatio > 1) ? (60 - 2 * whRatio) : 60

The filterFlag variable is derived as follows:

- If one or more of the following conditions are true, filterFlag is set equal to 0.

- predModeIntra is equal to INTRA_ANGULAR2, INTRA_ANGULAR34 or INTRA_ANGULAR66

- refIdx is not equal to 0

- IntraSubPartitionsSplitType is not equal to ISP_N O _SPLIT and cIdx is equal to 0 and predModeIntra is greater than or equal to INTRA_ANG<u>L<a r>34 and nW is greater than 8

- IntraSubPartitionsSplitType is not equal to ISP_N OR _SPLIT and cIdx is equal to 0 and predModeIntra is less than INTRA_ANGULAR34 and nH is greater than 8.

- Otherwise, the following applies:

- The variable minDistVerHor is set equal to Min(Abs(predModeIntra - 50), Abs(predModeIntra - 18)). - The variable intraHorVerDistThres[nTbS] is specified in Table 8-4.

- The filterFlag variable is derived as follows:

- If minDistVerHor is greater than intraHorVerDistThres[nTbS] or wideAngle is equal to 1, filterFlag is set equal to 1.

- Otherwise, filterFlag is set equal to 0.

Table 8-4 - intraHorVerDistThres[nTbS] specification for various nTbS transform block sizes

| intraHorVerDistThres[nTbS] |16_________| J 4 __________\_2___________ |_0___________ |_0_____________ |_0____________ | Fig. 6 illustrates the 93 prediction directions, where the dashed directions are associated with wide-angle modes that only apply to non-square blocks.

Table 8-5 specifies the mapping table between predModeIntra and the angle parameter intraPredAngle.

If cldx is not equal to 0, and subWidthC is greater than subHeightC, the following applies:

- If predModeIntra is greater than or equal to 34, intraPredAngle is set equal to intraPredAngle >> 1 - Otherwise, intraPredAngle is set equal to intraPredAngle << 1

The inverse angle parameter invAngle is derived based on intraPredAngle as follows:

/ 256*32 \

invAngle = RoundMntiaPrsdAngW

The interpolation filter coefficients fC[phase][j] and fG[phase][j] with phase = 0..31 and j = 0..3 are specified in Table 8-6.

Table 8-6 - Specification of interpolation filter coefficients fC and fG

The values of the prediction samples predSamples[x][y], with x = 0..nTbW - 1, y = 0..nTbH - 1 are derived as follows:

- If predModeIntra is greater than or equal to 34, the following ordered stages apply:

3. The reference sample array ref[x] is specified as follows:

- The following applies:

ref[x] = p[-1 - refIdx x][-1 - refIdx], with x = 0..nTbW refIdx

- If intraPredAngle is less than 0, the main reference sample array is extended as follows: - When (nTbH * intraPredAngle) >> 5 is less than -1,

ref[x] = p[-1 - refIdx][-1 - refIdx ((x * invAngle 128) >> 8)],

with x = -1..(nTbH * intraPredAngle) >> 5

ref[((nTbH * intraPredAngle) >> 5) - 1] = ref[(nTbH * intraPredAngle) >> 5]

ref[nTbW 1 refIdx] = ref[nTbW refIdx]

- Otherwise,

ref[x] = p[-1 - refIdx x][-1 - refIdx], with x = nTbW 1 refIdx..refW refIdx

ref[-1] = ref[0]

- The additional samples ref[refW refIdx x] with x = 1..(Max(1, nTbW/nTbH) * refIdx 1) are derived as follows:

ref[refW refIdx x] = p[-1 refW][-1 - refIdx]

4. The values of the prediction samples predSamples[x][y], with x = 0..nTbW - 1, y = 0..nTbH - 1 are derived as follows:

- The index variable iIdx and the multiplication factor iFact are derived as follows:

iIdx = ((y 1 refIdx) * intraPredAngle) >> 5 refIdx

iFact = ((y 1 refIdx) * intraPredAngle) & 31

- If cIdx is equal to 0, the following applies:

- The coefficients of the interpolation filter fT[j] with j = 0..3 are derived as follows:

fT[j] = filterFlag ? fG[iFact][j] : fC[iFact][j]

- The value of the prediction samples predSamples[x][y] is derived as follows:

predSamples[x][y]=CliplY(((Sf=ftfT[I ] *r e f [ s+ ildx+- i ])32)» 6)

- Otherwise (cIdx is not equal to 0), depending on the value of iFact, the following applies:

- If iFact is not equal to 0, the value of the prediction samples predSamples[x][y] is derived as follows: predSamples[x][y] =

((32 - iFact) * ref[x iIdx 1] iFact * ref[x iIdx 2] 16) >> 5

- Otherwise, the value of the prediction samples predSamples[x][y] is derived as follows: predSamples[x][y] = ref[x iIdx 1]

- Otherwise (predModeIntra is less than 34), the following ordered steps apply:

3. The reference sample array ref[x] is specified as follows:

- The following applies:

ref[x] = p[-1 - refIdx][-1 - refIdx x], with x = 0..nTbH refIdx

- If intraPredAngle is less than 0, the main reference sample array is extended as follows: - When (nTbW * intraPredAngle) >> 5 is less than -1,

ref[x] = p[-1 - refIdx ((x * invAngle 128) >> 8)][-1 - refIdx],

with x = -1..(nTbW * intraPredAngle) >> 5

ref[((nTbW * intraPredAngle) >> 5) - 1] =

ref[(nTbW * intraPredAngle) >> 5] (8-145)

ref[nTbG 1 refIdx] = ref[nTbH refIdx]

- Otherwise,

ref[x] = p[-1 - refIdx][-1 - refIdx x], with x = nTbH 1 refIdx..refH refIdx

ref[-1] = ref[0]

- the additional samples ref[refH refIdx x] with x = 1..(Max(1, nTbW/nTbH) * refIdx 1) are derived as follows: ref[refH refIdx x] = p[-1 refH][-1 - refIdx]

4. The values of the prediction samples predSamples[x][y], with x = 0..nTbW - 1, y = 0..nTbH - 1 are derived as follows:

- the index variable iIdx and the multiplication factor iFact are derived as follows:

iIdx = ((x 1 refIdx) * intraPredAngle) >> 5

iFact = ((x 1 refIdx) * intraPredAngle) & 31

- if cIdx is equal to 0, the following applies:

- the coefficients of the interpolation filter fT[j] with j = 0..3 are derived as follows:

fT[j] = filterFlag ? fG[iFact][j] : fC[iFact][j]

- the value of the prediction samples predSamples[x][y] is derived as follows:

predSamples[x][y] = CMp1Y(((2f=afT [ i ] * re f[? -H iId s i ] ) 32) » 6)

- otherwise (cIdx is not equal to 0), depending on the value of iFact, the following applies:

- If iFact is not equal to 0, the value of the prediction samples predSamples[x][y] is derived as follows:

predSamples[x][y] =

((32 - iFact) * ref[y iIdx 1] iFact * ref[y iIdx 2] 16) >> 5

- otherwise, the value of the prediction samples predSamples[x][y] is derived as follows:

predSamples[x][y] = ref[y iIdx 1]

In particular, the following methods and embodiments of predictive coding of a current block implemented by a decoding or encoding device. The decoding device may be the video decoder 30 of FIG. 1A, or the decoder 30 of FIG. 3. The encoding device may be the video encoder 20 of FIG. 1A or the encoder 20 of FIG. 2.

According to one embodiment 1200 (see FIG. 12A ), when the value of idc_chrom_format indicates 4:2:2 chroma format, a chroma intra prediction mode (intraPredModeC) 1203 is derived from a look-up table (LUT) 1202 using an initial intra prediction mode of the chroma component. The value of the initial intra prediction mode of the chroma component may be equal to the value of the luma intra prediction mode intraPredModeY. Table 2, Table 3, Table 8-2 or Table 8-3 give an example between the initial intra prediction mode value of chroma component intra_chroma_pred_mode[xCb][yCb] and the luma intra prediction mode value intraPredModeY IntraPredModeY[xCb cbWidth/2][yCb cbHeight/2].

The example for lookup table 1202 is table 5 or table 8-4. The lookup table includes 67 entries, with index 0-66.

After performing wide-angle assignment 1204 in chroma intra prediction mode 1203, a modified chroma intra prediction mode is obtained. A parameter 1205 intraPredAngle is obtained based on the modified chroma intra prediction mode. For example, using modified chroma intra prediction mode as predModeIntra, intraPredAngle 1205 is obtained from Table 1. The predicted samples of chroma component are obtained by performing directional chroma intra prediction1206 based on the parameter intraPredAngle.

According to an example 1210 not part of the invention (see FIG. 12B ), the wide angle assignment 1212 is performed in the luma intra prediction mode 1211 intraPredModeY to obtain a modified intraPredModeY. When the value of idc_chrom_format indicates 4:2:2 chroma format, a chroma intra prediction mode 1214 (intraPredModeC) is derived from a look-up table (LUT) 1213 using the modified intraPredModeY. The look-up table 1213 may have 95 entries, with index 0-94.

A 1215 intraPredAngle parameter is obtained based on the chroma intra prediction mode. For example, by using the chroma intra prediction mode as the predModeIntra, intraPredAngle is obtained from Table 1. The predicted samples of the chroma component are obtained by performing directional chroma intra prediction based on the intraPredAngle parameter.

Embodiment 1300 includes the following steps: Step 1301, the device obtains the value of a luma intra prediction mode (intraPredModeY). For example, the device obtains the value of intraPredModeY by analyzing a bitstream. Step 1302, the device obtains the initial chroma component intra prediction mode (IntraPredModeC) based on the value of the luma intra prediction mode (intraPredModeY), for example, based on Table 2, Table 3, Table 8-2, or Table 8-3. Step 1303, the device derives a chroma intra prediction mode (intraPredModeC) from a look-up table (LUT) using the initial chroma component intra prediction mode (intraPredModeC) when the chroma aspect ratio is 4:2:2. In the example in Table 8-4, the initial intra prediction mode of the chroma component is mode X, a chroma intra prediction mode (intraPredModeC) is mode Y. That means the original intraPredModeC is adjusted to get the intraPredModeC.

Step 1304 includes performing a wide-angle mapping in the intra chroma prediction mode (intraPredModeC) to obtain a modified intraPredModeC. As described above, wide-angle mapping is included for non-square blocks (nW is not equal to nH):

If all of the following conditions are true, wideAngle is set equal to 1 and predModeIntra is set equal to (predModeIntra 65):

nW is greater than nH

predModeIntra is greater than or equal to 2

predModeIntra is less than (whRatio > 1) ? (8 2 * whRatio) : 8

Otherwise, if all of the following conditions are true, wideAngle is set equal to 1 and predModeIntra is set equal to (predModeIntra - 67):

nH is greater than nW

predModeIntra is less than or equal to 66

predModeIntra is greater than (whRatio > 1) ? (60 - 2 * whRatio) : 60

Step 1305 includes obtaining an intraPredAngle parameter for the chroma component based on the modified intraPredModeC. For example, using modified intraPredModeC as the predModeIntra, intraPredAngle 1215 is obtained from Table 1. Step 1306 includes obtaining predicted samples of the chroma component based on the intraPredAngle parameter.

Detailed information of this embodiment 1300 is shown in the above-mentioned embodiments.

Fig. 14 illustrates embodiments of a device 1400. The device 1400 may be a video decoder 30 of Fig. 1A, or a decoder 30 of Fig. 3, or it may be a video encoder 20 of Fig. 1A, or an encoder 20 of Fig. 2. The device 1400 may be used to implement embodiment 1200, 1210, 1300, and the other embodiments described above.

The directional intra prediction device for the chroma component of an image includes a obtaining unit 1401, a derivation unit 1402 and an assignment unit 1403.

The obtaining unit 1401, configured to obtain an initial intra prediction mode of the chroma component. The derivation unit 1402, configured to derive a chroma intra prediction mode (intraPredModeC) from a look-up table (LUT) using the initial intra prediction mode of the chroma component, the chroma component having different subsampling ratios in horizontal and vertical directions. The derivation unit 1402 may be used to derive the chroma intra prediction mode IntraPredModeC [xCb] [yCb] by using intra_chroma_pred_mode [xCb] [yCb] and IntraPredModeY [xCb cbWidth/2] [yCb cbHeight/2] as specified in Table 2 and Table 83.

The mapping unit 1403, configured to perform wide-angle mapping in the chroma intra prediction mode (intraPredModeC) to obtain a modified intraPredModeC. As an example, the mapping unit 1403 performs wide-angle mapping in an original intra prediction mode (predModeIntra) to obtain a modified predModeIntra, where the value of the original predModeIntra is equal to the value of the chroma intra prediction mode (intraPredModeC).

The obtaining unit 1401, further configured to obtain an intraPredAngle parameter for the chroma component, for example, from a mapping table, based on the modified intraPredModeC; and obtain predicted samples of the chroma component based on the intraPredAngle parameter.

The obtaining unit 1401 may also be configured to obtain the value of a luma intra prediction mode (intraPredModeY) from a bit stream, and then obtain the initial intra prediction mode of the chroma component based on the value of the luma intra prediction mode (intraPredModeY).

The chroma mode derivation process according to the proposed method is endowed with beneficial effects compared to conventional approaches. One of these effects is that embodiments of the invention provide the minimum number of entries in the LUT which is used to determine the chroma intra prediction mode from the initial luma intra prediction mode. This is achieved by the order of the steps performed, i.e. by the mapping of the chrominance intra prediction mode to the luminance mode which is performed before the wide angle mapping. When applying chroma to luma LUT without wide angle mapping, it is necessary to specify the mapping only for the square block shape, thus limiting the required LUT entries to 67.

Furthermore, in an example not forming part of the claimed invention, the derivation of the chrominance mode does not require obtaining the shape of the simultaneously located luminance block. In the conventional method, the luminance intra prediction address assignment that is the result of the wide angle assignment process would require considering the aspect ratio of the luminance block as well. The reason for this dependency is that the wide angle assignment process requires information about the aspect ratio of the block to determine the value of the assigned intra prediction mode. In embodiments of this invention, the wide angle assignment is not performed for the input luminance intra prediction mode and therefore the input luminance intra prediction mode could be obtained by bitstream parsing. Since the partitioning structure of the luminance component is not required to be handled, the decoding latency is improved if the suggested order of steps is used.

The following provides an explanation of the applications of the encoding method as well as the decoding method as shown in the above-mentioned embodiments, and a system using them.

15 is a block diagram showing a content delivery system 3100 for performing a content distribution service. This content delivery system 3100 includes the capture device 3102, the terminal device 3106, and optionally includes the display device 3126. The capture device 3102 communicates with the terminal device 3106 via the communication link 3104. The communication link may include the communication channel 13 described above. The communication link 3104 includes, but is not limited to, WIFI, Ethernet, cable, wireless (3G/4G/5G), USB, or any combination thereof, or the like.

The capture device 3102 generates data and may encode the data by the encoding method as shown in the above embodiments. Alternatively, the capture device 3102 may distribute the data to a transmission server (not shown in the figures), and the server encodes the data and transmits the encoded data to the terminal device 3106. The capture device 3102 includes, but is not limited to, a camera, smartphone or Pad, computer or laptop, video conferencing system, PDA, vehicle-mounted device, or a combination of any of them, or the like. For example, the capture device 3102 may include the source device 12 as described above. When the data includes video, the video encoder 20 included in the capture device 3102 may actually perform the video encoding processing. When the data includes audio (i.e., voice), an audio encoder included in the capture device 3102 may actually perform the audio encoding processing. For some practical scenarios, the capture device 3102 distributes the encoded audio data and video data by multiplexing them together. For other practical scenarios, for example, in the video conference system, the encoded audio data and the encoded video data are not multiplexed. The capture device 3102 distributes the encoded audio data and the encoded video data to the terminal device 3106 separately.

In content delivery system 3100, terminal device 310 receives and plays back the encoded data. Terminal device 3106 could be a device capable of receiving and retrieving data, such as a smartphone or Pad 3108, computer or laptop 3110, network video recorder (NVR)/digital video recorder (DVR) 3112, TV 3114, set-top box (STB) 3116, video conferencing system 3118, video surveillance system 3120, personal digital assistant (PDA) 3122, vehicle-mounted device 3124, or a combination of any of these, or the like capable of decoding the aforementioned encoded data. For example, terminal device 3106 may include destination device 14 as described above. When the encoded data includes video, the video decoder 30 included in the terminal device is prioritized to perform video decoding. When the encoded data includes audio, an audio decoder included in the terminal device is prioritized to perform audio decoding processing.

For a terminal device with its display device, for example, smartphone or Pad 3108, computer or laptop 3110, network video recorder (NVR)/digital video recorder (DVR) 3112, TV 3114, personal digital assistant (PDA) 3122, or vehicle mounted device 3124, the terminal device may feed the decoded data to its display device. For a terminal device equipped without a display device, for example, STB 3116, video conferencing system 3118, or video surveillance system 3120, it contacts an external display device 3126 to receive and display the decoded data.

When each device of this system performs encoding or decoding, the image encoding device or the image decoding device may be used, as shown in the above-mentioned embodiments.

Fig. 16 is a diagram showing a structure of an example of the terminal device 3106. After the terminal device 3106 receives the stream from the capture device 3102, the protocol processing unit 3202 parses the transmission protocol of the stream. The protocol includes, but is not limited to, real-time streaming protocol (RTSP), hypertext transfer protocol (HTTP), HTTP live streaming protocol (HLS), MPEG-DASH, real-time transport protocol (RTP), real-time messaging protocol (RTMP), or any combination thereof, or the like. After the protocol processing unit 3202 processes the stream, the stream file is generated. The file is sent to a demultiplexing unit 3204. The demultiplexing unit 3204 may separate the multiplexed data into the encoded audio data and the encoded video data. As described above, for some practical scenarios, for example, in the video conferencing system, the encoded audio data and the encoded video data are not multiplexed. In this situation, the encoded data is transmitted to the video decoder 3206 and the audio decoder 3208 without passing through the demultiplexing unit 3204.

Through the demultiplexing processing, the video elementary stream (ES), the audio ES, and optionally the subtitles are generated. The video decoder 3206, which includes the video decoder 30 as explained in the aforementioned embodiments, decodes the video ES by the decoding method as shown in the aforementioned embodiments to generate a video frame, and feeds this data to the synchronous unit 3212. The audio decoder 3208 decodes the audio ES to generate an audio frame and feeds this data to the synchronous unit 3212. Alternatively, the video frame may be stored in a buffer (not shown in FIG. Y) before being fed to the synchronous unit 3212. Similarly, the audio frame may be stored in a buffer (not shown in FIG. Y) before being fed to the synchronous unit 3212.

The synchronous unit 3212 synchronizes the video frame and the audio frame, and delivers the video/audio to a video/audio display device 3214. For example, the synchronous unit 3212 synchronizes the presentation of the video and audio information. The information may be encoded in the syntax using time stamps relative to the presentation of encoded audio and visual data and time stamps relative to the delivery of the data stream itself.

If subtitles are included in the stream, the subtitle decoder 3210 decodes the subtitle and synchronizes it with the video frame and the audio frame, and supplies the video/audio/subtitle to a video/audio/subtitle display device 3216.

The present invention is not limited to the above-mentioned system, and either the image coding device or the image decoding device in the above-mentioned embodiments may be incorporated into another system, for example, an automobile system.

Mathematical Operators

The mathematical operators used in this application are similar to those used in the C programming language. However, the results of integer division and arithmetic shift operations are more precisely defined, and additional operations such as exponentiation and division on real values are defined. Numbering and counting conventions generally start from 0, for example, “the first” is equivalent to the 0-th, “the second” is equivalent to the 1-th, etc.

Arithmetic Operators

The following arithmetic operators are defined as follows:

+ Add

- Subtraction (as a two-argument operator) or negation (as a unary prefix operator)

* Multiplication, including matrix multiplication

xy Exponentiation. Specifies x raised to the power of y. In other contexts, this notation is used for superscripts not intended to be interpreted as exponentiation.

/ Integer division with truncation of the result towards zero. For example, 7/4 and -7/-4 are truncated to 1 and -7/4 and 7/-4 are truncated to -1.

It is used to indicate division in mathematical equations where truncation or rounding is not intended.

It is used to indicate division in mathematical equations where truncation or division is not intended.

rounding.

The summation of f(i) with i takes all integer values from x to y, including y.

x % y Modulus. Remainder of x divided by y, defined only for integers x and y with x>=0 and y>0.

Logical Operators

The following logical operators are defined as follows:

x && y Logical boolean "and" of x and y

x | | y Boolean logical "or" of x and y

! Boolean logical "not"

X ? y: z If x is TRUE or not equal to 0, evaluates to the value of y; otherwise, evaluates to the value of z. Relational Operators

The following relational operators are defined as follows:

> Greater than

> = Greater than or equal to

< Less than

<= Less than or equal to

= = Equal to

! = Not equal to

When a relational operator is applied to a syntax element or variable that has been assigned the value “na” (not applicable), the value “na” is treated as a distinct value for the syntax element or variable. The value “na” is considered not to be equal to any other value.

Bitwise Operators

The following bitwise operators are defined as follows:

& Bitwise “and”. When operating on integer arguments, operates on a two’s complement representation of the integer value. When operating on a binary argument that contains fewer bits than another argument, the shorter argument is extended by adding more significant bits equal to 0.

| Bitwise “or”. When operating on integer arguments, operates on a two’s complement representation of the integer value. When operating on a binary argument that contains fewer bits than another argument, the shorter argument is extended by adding more significant bits equal to 0.

<a>Bitwise “exclusive or”. When operating on integer arguments, operates on a two's complement representation of the integer value. When operating on a binary argument that contains fewer bits than another argument, the shorter argument is extended by adding more significant bits equal to 0.

x >> y Arithmetic shift right of a two's complement integer representation of x by y binary digits. This function is defined only for non-negative integer values of y. The bits shifted to the most significant bits (MSB) as a result of the right shift have a value equal to the MSB of x before the shift operation.

x << y Arithmetic shift left of a two's complement integer representation of x by y binary digits. This function is defined only for non-negative integer values of y. Bits shifted to the least significant bits (LSB) as a result of the left shift have a value equal to 0.

Assignment Operators

The following arithmetic operators are defined as follows:

= Assignment operator

+ Increment, that is, x is equivalent to x = x 1; when used on an array index, it evaluates to the value of the variable before the increment operation.

- - Decrement, that is, x- - is equivalent to x = x - 1; when used on an array index, it evaluates the value of the variable before the decrement operation.

+ = Increase by the specified amount, that is, x = 3 is equivalent to x = x 3, and x = (-3) is equivalent to x = x (-3).

- = Decrease by the specified amount, that is, x - = 3 is equivalent to x = x - 3, and x - = (-3 ) is equivalent to x = x - (-3).

Interval notation

The following notation is used to specify a range of values:

x = y..z x takes integer values starting from y to z, inclusive, where x, y, and z are integers and z is greater than y.

Mathematical Functions

The following mathematical functions are defined:

( x ; x >= O

Abs(x) = t - x

ASin(x) the inverse trigonometric sine function, operating on an argument x that is in the range -1.0 to 1.0, inclusive, with an output value in the range -n 2 to n 2, inclusive, in units of radians Atan(x) the inverse trigonometric tangent function, operating on an argument x, with an output value in the range -n 2 to n 2, inclusive, in units of radians

Ceil(x) the smallest integer greater than or equal to x.

Clip1Y(x) = Clip3(0, (1 << BitDepthY) - 1, x)

Clip1c(x) = Clip3(0, (1 << BitDepthC) - 1, x)

x ; z < x

and ; s > and

Clip3(x, y, z) = £ ; otherwise

Cos(x) is the trigonometric cosine function that operates on an argument x in units of radians.

Floor(x) the largest integer less than or equal to x.

Ln(x) the natural logarithm of x (the logarithm to base e, where e is the natural logarithm to the constant base 2.718 281 828 ...).

Log2(x) is the base 2 logarithm of x.

Log10(x) is the base 10 logarithm of x.

Round (x) = Sign (x) * Floor (Abs (x) 0.5)

Sen(x) is the trigonometric sine function that operates on an argument x in units of radians

Root(x) = V *

Exchange(x, y) = (y, x)

Tan(x) the trigonometric tangent function that operates on an argument x in units of radians Order of precedence of the operation

When an order of precedence in an expression is not explicitly indicated by the use of parentheses, the following rules apply:

- Operations of higher precedence are evaluated before any operations of lower precedence. - Operations of the same precedence are evaluated sequentially from left to right.

The following table specifies the precedence of operations from highest to lowest; a higher position in the table indicates a higher precedence.

For those operators that are also used in the C programming language, the order of precedence used in this specification is the same as that used in the C programming language.

Table: precedence of operations from highest (at the top of the table) to lowest (at the bottom of the table)

Text description of logical operations

In the text, a logical operations statement would be described mathematically as follows: if( condition 0 )

statement 0

else if( condition 1 )

statement 1

else /* informative remark on remaining condition */

statement n

can be described as follows:

... as follows / ... the following applies:

- If condition 0, statement 0

- Otherwise, if condition 1, statement 1

- Otherwise (informative remark on remaining condition), statement n

Each "if ... Otherwise, if ... Otherwise, ..." statement in the text is introduced with "... as follows" or "... the following applies" followed immediately by "If ... ". The last condition of an "If ... Otherwise, If ... Otherwise, ..." is always an " Otherwise, ...". Interleaved "If ... Otherwise, If ... Otherwise, ..." statements can be identified by matching "... as follows" or "... the following applies" with the trailing " Otherwise, ...".

In the text, a logical operations instruction would be described mathematically as follows:

If(condition 0a && condition 0b)

statement 0

else if(condition 1a | | condition 1b)

statement 1

else

statement n

can be described as follows:

...a s follows /... the following applies:

- If all the following conditions are true, statement 0:

- condition 0a

- condition 0b

- Otherwise, if one or more of the following conditions are true, statement 1:

- condition 1a

- condition 1b

- Otherwise, statement n.

In the text, a logical operations statement would be described mathematically as follows: if( condition 0 )

statement 0

if( condition 1 )

statement 1

can be described as follows:

When condition 0, statement 0

When condition 1, statement 1

Although embodiments of the invention have been described primarily on the basis of video coding, it should be noted that embodiments of the coding system 10, the encoder 20 and the decoder 30 (and hence the system 10) and the other embodiments described herein may also be configured for image processing or coding, i.e., processing or coding an individual image independently of any preceding or consecutive images as in video coding. In general, only the inter prediction (encoder) and decoder units 244 (344) may not be available in case the image processing encoding is limited to a single image 17. All other functionalities (also called tools or technologies) of the video encoder 20 and video decoder 30 may equally be used for still image processing, e.g., residual calculation 204/304, transform 206, quantization 208, inverse quantization 210/310, transform 212/312 (inverse), partitioning 262/362, intra prediction 254/354 and/or loop filtering 220, 320 and entropy encoding 270 and entropy decoding 304.

Embodiments of, for example, encoder 20 and decoder 30, and the functions described herein, for example, with reference to encoder 20 and decoder 30, may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored on a computer-readable medium or transmitted via communication media as one or more instructions or code and executed by a hardware-based processing unit. Computer-readable media may include computer-readable storage media, which corresponds to a tangible medium, such as a data storage media, or communication media, including any medium that facilitates the transfer of a computer program from one location to another, for example, in accordance with a communication protocol. Thus, computer-readable media may generally correspond to (1) tangible computer-readable storage media that is non-transitory or (2) a communication medium such as a signal or carrier wave. Data storage media may be any available medium that can be accessed by one or more computers or one or more processors to retrieve instructions, code, and/or data structures for implementing the techniques described in this disclosure. A computer program product may include a computer-readable medium.

By way of example, and not limitation, such computer-readable storage media may comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, flash memory, or any other medium that can be used to store the desired program code in the form of instructions or data structures and that can be accessed by a computer. In addition, any connection is properly referred to as a computer-readable medium. For example, if instructions are transmitted from a website, server, or other remote source using coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio, and microwave, then coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included within the definition of medium. However, it should be understood that computer-readable storage media and data storage media do not include connections, carrier waves, signals or other transient media, but are directed to tangible and non-transient storage media. Disk and disc as used herein include compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk and Blu-ray disc, where discs generally reproduce data magnetically, while disks reproduce data optically with lasers. Combinations of the above should also be included within the scope of computer-readable media.

The instructions may be executed by one or more processors, such as one or more digital signal processors (DSPs), general purpose microprocessors, application specific integrated circuits (ASICs), field programmable logic arrays (FPGAs), or other equivalent integrated or discrete logic circuits. Accordingly, the term “processor,” as used herein, may refer to any of the foregoing structures or any other structure suitable for implementing the techniques described herein. Furthermore, in some aspects, the functionality described herein may be provided within dedicated hardware and/or software modules configured to encode and decode, or incorporated into a combined codec. Furthermore, the techniques could be implemented entirely in one or more circuits or logic elements.

The techniques of this disclosure may be implemented in a wide variety of devices or apparatus, including a wireless telephone, an integrated circuit (IC), or an array of ICs (e.g., a chipset). Various components, modules, or units are described in this disclosure to emphasize the functional aspects of devices configured to perform the described techniques, but do not necessarily require implementation by different hardware units. Rather, as described above, various units may be combined into one codec hardware unit or provided by a collection of interoperable hardware units, including one or more processors as described above, together with suitable software and/or firmware.

Claims (12)

CLAIMS 1. A directional intra prediction method for the chroma component of an image, comprising: obtaining an initial intra prediction mode of the chroma component based on a luma intra prediction mode value (intraPredModeY) of a luma component using a first look-up table (LUT); deriving a chroma intra prediction mode (intraPredModeC) from a second LUT using the initial intra prediction mode of the chroma component when the chroma format of the chroma component is defined as YUV 4:2:2, the chroma component having different subsampling ratios in horizontal (SubWidthC) and vertical (SubHeightC) directions, wherein the second LUT has 67 entries, the index for the second LUT is 0-66, and each index is associated with an angle of an intra prediction direction; Perform wide angle mapping in chroma intraprediction mode (intraPredModeC) to obtain a modified intraPredModeC using a block aspect ratio of the luma component to ensure that the intraprediction directions for the chroma component and the luma component match; obtain an intraPredAngle parameter for the chroma component based on the modified intraPredModeC; and obtain predicted samples of the chroma component based on the intraPredAngle parameter. 2. The method of claim 1, wherein the method further comprises: obtaining the value of the luma intra prediction mode (intraPredModeY) of a bit stream; 3. The method according to claim 1 or 2, wherein performing wide-angle allocation in the chroma intra prediction mode (intraPredModeC) to obtain the intraPredModeC comprises: performing wide-angle allocation in an original intra prediction mode (predModeIntra) to obtain a modified predModeIntra, wherein the value of the original predModeIntra is equal to the value of the chroma intra prediction mode (intraPredModeC). 4. The method of claim 3, wherein obtaining the IntraPredAngle parameter based on IntraPredModeC comprises: obtaining the intraPredAngle parameter for the chroma component from a mapping table using the modified predModeIntra. 5. The method of any of claims 1-4, wherein the method further comprises: performing a clipping operation in the intra-prediction derived chroma mode (intraPredModeC). 6. The method of any of claims 1-5, wherein the wide angle assignment is performed for the luma intraprediction mode (intraPredModeY). 7. The method of claim 6, wherein the wide angle assignment is performed for the luma intra prediction mode (intraPredModeY) using an aspect ratio of a luma component and resulting in IntraPredModeFinalY. 8. The method of any of claims 1-7, wherein the initial intra prediction mode of the chroma component is obtained using intra_chroma_mode[xCb][yCb] and IntraPredModeY[xCb cbWidth /2][yCb cbHeight /2] as specified in the first LUT. wherein when sps_cclm_enabled_flag is equal to 0, the first LUT includes: where when sps_cclm_enabled_flag is equal to 1, the first LUT includes: 9. The method of claim 1, wherein the assignment between the index and the corresponding angle parameter is shown below: where predModeIntra represents the index, and the parameter intraPredAngle represents the angle parameter of the corresponding index; where the parameter intrePredAngle is used to obtain the predicted samples of the chroma component. 10. The method of claim 3, wherein in the non-square blocks (nW is not equal to nH), performing wide angle assignment in the original intra prediction mode (predModeIntra) to obtain the modified predModeIntra comprises: if all of the following conditions are true, wideAngle is set equal to 1 and predModeIntra is set equal to (predModeIntra 65): nW is greater than nH predModeIntra is greater than or equal to 2 predModeIntra is less than (whRatio > 1) ? (8 2 * whRatio) : 8 Otherwise, if all of the following conditions are true, wideAngle is set equal to 1 and predModeIntra is set equal to (predModeIntra - 67): nH is greater than nW predModeIntra is less than or equal to 66 predModeIntra is greater than (whRatio > 1) ? (60 - 2 * whRatio) : 60, where the variable whRatio is set equal to Abs(Log2(nW/nH)); where whRadio is the aspect ratio of the luma component block. 11. An encoder (20) or a decoder (30) comprising processing circuits for carrying out the method according to any one of claims 1 to 10. 12. A computer program product comprising program code for performing the method according to any one of claims 1 to 10.